Glossary of engineering

Short description: List of definitions of terms and concepts commonly used in the study of engineering

This glossary of engineering terms is a list of definitions about the major concepts of engineering. Please see the bottom of the page for glossaries of specific fields of engineering.

## Contents

* 1 A
* 2 B
* 3 C
* 4 D
* 5 E
* 6 F
* 7 G
* 8 H
* 9 I
* 10 J
* 11 K
* 12 L
* 13 M
* 14 N
* 15 O
* 16 P
* 17 Q
* 18 R
* 19 S
* 20 T
* 21 U
* 22 V
* 23 W
* 24 X
* 25 Y
* 26 Z
* 27 See also
* 28 Notes
* 29 References

## A

Absolute electrode potential
In electrochemistry, according to an IUPAC definition,[1] is the electrode potential of a metal measured with respect to a universal reference system (without any additional metal–solution interface).
Absolute pressure
Is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure.
Absolute zero
Is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as 0. Absolute zero is the point at which the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. The theoretical temperature is determined by extrapolating the ideal gas law; by international agreement, absolute zero is taken as −273.15° on the Celsius scale (International System of Units),[2][3] which equals −459.67° on the Fahrenheit scale (United States customary units or Imperial units).[4] The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.
Absorbance
Absorbance or decadic absorbance is the common logarithm of the ratio of incident to transmitted radiant power through a material, and spectral absorbance or spectral decadic absorbance is the common logarithm of the ratio of incident to transmitted spectral radiant power through a material.[5]
AC power
Electric power delivered by alternating current; common household power is AC.
Acceleration
The rate at which the velocity of a body changes with time, and the direction in which that change is acting.
Acid
A molecule or ion capable of donating a hydron (proton or hydrogen ion H+), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid).[6]
Acid–base reaction
A chemical reaction that occurs between an acid and a base, which can be used to determine pH.
Acid strength
In strong acids, most of the molecules give up a hydrogen ion and become ionized.
Acoustics
The scientific study of sound.
Activated sludge
A type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.
Activated sludge model
A generic name for a group of mathematical methods to model activated sludge systems.
Active transport
In cellular biology, active transport is the movement of molecules across a membrane from a region of their lower concentration to a region of their higher concentration—against the concentration gradient. Active transport requires cellular energy to achieve this movement. There are two types of active transport: primary active transport that uses ATP, and secondary active transport that uses an electrochemical gradient. An example of active transport in human physiology is the uptake of glucose in the intestines.
Actuator
A device that accepts 2 inputs (control signal, energy source) and outputs kinetic energy in the form of physical movement (linear, rotary, or oscillatory). The control signal input specifies which motion should be taken. The energy source input is typically either an electric current, hydraulic pressure, or pneumatic pressure. An actuator can be the final element of a control loop
Adenosine triphosphate
A complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer.[7]
Adhesion
The tendency of dissimilar particles or surfaces to cling to one another (cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
Adiabatic process
A process where no heat energy is lost to outside space.
Adiabatic wall
A barrier through which heat energy cannot pass.
Aerobic digestion
A process in sewage treatment designed to reduce the volume of sewage sludge and make it suitable[8] for subsequent use.[9]
Aerodynamics
The study of the motion of air, particularly its interaction with a solid object, such as an airplane wing. It is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields.
Aerospace engineering
Is the primary field of engineering concerned with the development of aircraft and spacecraft.[10] It has two major and overlapping branches: Aeronautical engineering and Astronautical Engineering. Avionics engineering is similar, but deals with the electronics side of aerospace engineering.
Afocal system
An optical system that produces no net convergence or divergence of the beam, i.e. has an infinite effective focal length.[11]
Agricultural engineering
The profession of designing machinery, processes, and systems for use in agriculture.
Albedo
A measure of the fraction of light reflected from an astronomical body or other object.
Alkane
An alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon–carbon bonds are single.[12]
Alkene
An unsaturated hydrocarbon that contains at least one carbon–carbon double bond.[13] The words alkene and olefin are often used interchangeably.
Alkyne
Is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond.[14] The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula CnH2n−2.
Alloy
is a combination of metals or of a metal and another element. Alloys are defined by a metallic bonding character.[15]
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α.
Alternating current
Electrical current that regularly reverses direction.
Alternative hypothesis
In statistical hypothesis testing, the alternative hypothesis (or maintained hypothesis or research hypothesis) and the null hypothesis are the two rival hypotheses which are compared by a statistical hypothesis test. In the domain of science two rival hypotheses can be compared by explanatory power and predictive power.
Ammeter
An instrument that measures current.
Amino acids
Are organic compounds containing amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid.[16][17][18] The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways.[19]
Amorphous solid
An amorphous (from the Greek a, without, morphé, shape, form) or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.
Ampere
The SI unit of current flow, one coulomb per second.
Amphoterism
In chemistry, an amphoteric compound is a molecule or ion that can react both as an acid as well as a base.[20] Many metals (such as copper, zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Amphoterism depends on the oxidation states of the oxide. Al2O3 is an example of an amphoteric oxide.
Amplifier
A device that replicates a signal with increased power.
Amplitude
The amplitude of a periodic variable is a measure of its change over a single period (such as time or spatial period). There are various definitions of amplitude, which are all functions of the magnitude of the difference between the variable's extreme values. In older texts the phase is sometimes called the amplitude.[21]
Anaerobic digestion
Is a collection of processes by which microorganisms break down biodegradable material in the absence of oxygen.[22] The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.
Angular acceleration
Is the rate of change of angular velocity. In three dimensions, it is a pseudovector. In SI units, it is measured in radians per second squared (rad/s2), and is usually denoted by the Greek letter alpha (α).[23]
Angular momentum
In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity—the total angular momentum of a system remains constant unless acted on by an external torque.
Angular velocity
In physics, the angular velocity of a particle is the rate at which it rotates around a chosen center point: that is, the time rate of change of its angular displacement relative to the origin (i.e. in layman's terms: how quickly an object goes around something over a period of time - e.g. how fast the earth orbits the sun). It is measured in angle per unit time, radians per second in SI units, and is usually represented by the symbol omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise.
Anion
Is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).[24]
Annealing (metallurgy)
A heat treatment process that relieves internal stresses.
Annihilation
In particle physics, annihilation is the process that occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons.[25] The total energy and momentum of the initial pair are conserved in the process and distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of such an original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed.[26]
Anode
The electrode at which current enters a device such as an electrochemical cell or vacuum tube.
ANSI
The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.[27] The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.
Anti-gravity
Anti-gravity (also known as non-gravitational field) is a theory of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift.
Applied engineering
Is the field concerned with the application of management, design, and technical skills for the design and integration of systems, the execution of new product designs, the improvement of manufacturing processes, and the management and direction of physical and/or technical functions of a firm or organization. Applied-engineering degreed programs typically include instruction in basic engineering principles, project management, industrial processes, production and operations management, systems integration and control, quality control, and statistics.[28]
Applied mathematics
Mathematics used for solutions of practical problems, as opposed to pure mathematics.
Arc length
Determining the length of an irregular arc segment is also called rectification of a curve. Historically, many methods were used for specific curves. The advent of infinitesimal calculus led to a general formula that provides closed-form solutions in some cases.
Archimedes' principle
States that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces and acts in the upward direction at the center of mass of the displaced fluid.[29] Archimedes' principle is a law of physics fundamental to fluid mechanics. It was formulated by Archimedes of Syracuse.[30]
Area moment of inertia
The 2nd moment of area, also known as moment of inertia of plane area, area moment of inertia, or second area moment, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The second moment of area is typically denoted with either an I for an axis that lies in the plane or with a J for an axis perpendicular to the plane. In both cases, it is calculated with a multiple integral over the object in question. Its dimension is L (length) to the fourth power. Its unit of dimension when working with the International System of Units is meters to the fourth power, m4.
Arithmetic mean
In mathematics and statistics, the arithmetic mean or simply the mean or average when the context is clear, is the sum of a collection of numbers divided by the number of numbers in the collection.[31]
Arithmetic progression
In mathematics, an arithmetic progression  (AP) or arithmetic sequence is a sequence of numbers such that the difference between the consecutive terms is constant. Difference here means the second minus the first. For instance, the sequence 5, 7, 9, 11, 13, 15, . . . is an arithmetic progression with common difference of 2.
Aromatic hydrocarbon
An aromatic hydrocarbon or arene[32] (or sometimes aryl hydrocarbon)[33] is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization. The term "aromatic" was assigned before the physical mechanism determining aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).
Arrhenius equation
The Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 1884 that Van 't Hoff's equation for the temperature dependence of equilibrium constants suggests such a formula for the rates of both forward and reverse reactions. This equation has a vast and important application in determining rate of chemical reactions and for calculation of energy of activation. Arrhenius provided a physical justification and interpretation for the formula.[34][35][36] Currently, it is best seen as an empirical relationship.[37]: 188 It can be used to model the temperature variation of diffusion coefficients, population of crystal vacancies, creep rates, and many other thermally-induced processes/reactions. The Eyring equation, developed in 1935, also expresses the relationship between rate and energy.
Artificial intelligence
(AI), is intelligence demonstrated by machines, unlike the natural intelligence displayed by humans and animals. Leading AI textbooks define the field as the study of "intelligent agents": any device that perceives its environment and takes actions that maximize its chance of successfully achieving its goals.[40] Colloquially, the term "artificial intelligence" is often used to describe machines (or computers) that mimic "cognitive" functions that humans associate with the human mind, such as "learning" and "problem solving".[41]
Assembly language
A computer programming language where most statements correspond to one or a few machine op-codes.
Atomic orbital
In atomic theory and quantum mechanics, an atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.[42] This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term atomic orbital may also refer to the physical region or space where the electron can be calculated to be present, as defined by the particular mathematical form of the orbital.[43]
Atomic packing factor
The percentage of the volume filled with atomic mass in a crystal formation.
Audio frequency
An audio frequency (abbreviation: AF), or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human. The SI unit of audio frequency is the hertz (Hz). It is the property of sound that most determines pitch.[44]
Austenitization
Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite.[45] The more open structure of the austenite is then able to absorb carbon from the iron-carbides in carbon steel. An incomplete initial austenitization can leave undissolved carbides in the matrix.[46] For some irons, iron-based metals, and steels, the presence of carbides may occur during the austenitization step. The term commonly used for this is two-phase austenitization.[47]
Automation
Is the technology by which a process or procedure is performed with minimum human assistance.[48] Automation[49] or automatic control is the use of various control systems for operating equipment such as machinery, processes in factories, boilers and heat treating ovens, switching on telephone networks, steering and stabilization of ships, aircraft and other applications and vehicles with minimal or reduced human intervention. Some processes have been completely automated.
Autonomous vehicle
A vehicle capable of driving from one point to another without input from a human operator.
Azimuthal quantum number
The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers which describe the unique quantum state of an electron (the others being the principal quantum number, following spectroscopic notation, the magnetic quantum number, and the spin quantum number). It is also known as the orbital angular momentum quantum number, orbital quantum number or second quantum number, and is symbolized as ℓ.

## B

Barometer
A device for measuring pressure.
Battery
Electrochemical cells that transform chemical energy into electricity.
Base
In chemistry, bases are substances that, in aqueous solution, release hydroxide (OH−) ions, are slippery to the touch, can taste bitter if an alkali,[50] change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, promote certain chemical reactions (base catalysis), accept protons from any proton donor, and/or contain completely or partially displaceable OH− ions.
Baud
Rate at which data is transferred in symbols/second; a symbol may represent one or more bits.
Beam
A structural element whose length is significantly greater than its width or height.
Beer–Lambert law
The Beer–Lambert law, also known as Beer's law, the Lambert–Beer law, or the Beer–Lambert–Bouguer law relates the attenuation of light to the properties of the material through which the light is travelling. The law is commonly applied to chemical analysis measurements and used in understanding attenuation in physical optics, for photons, neutrons or rarefied gases. In mathematical physics, this law arises as a solution of the BGK equation.
Belt
A closed loop of flexible material used to transmit mechancial power from one pulley to another.
Belt friction
Is a term describing the friction forces between a belt and a surface, such as a belt wrapped around a bollard. When one end of the belt is being pulled only part of this force is transmitted to the other end wrapped about a surface. The friction force increases with the amount of wrap about a surface and makes it so the tension in the belt can be different at both ends of the belt. Belt friction can be modeled by the Belt friction equation.[51]
Bending
In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or less, of the other two.[52]
Bending moment
In solid mechanics, a bending moment is the reaction induced in a structural element when an external force or moment is applied to the element, causing the element to bend.[53] [54] The most common or simplest structural element subjected to bending moments is the beam.
Benefit–cost analysis
Cost–benefit analysis (CBA), sometimes called benefit costs analysis (BCA), is a systematic approach to estimating the strengths and weaknesses of alternatives (for example in transactions, activities, functional business requirements); it is used to determine options that provide the best approach to achieve benefits while preserving savings.[55] It may be used to compare potential (or completed) courses of actions; or estimate (or evaluate) the value against costs of a single decision, project, or policy.
Bernoulli differential equation
In mathematics, an ordinary differential equation of the form:

y′+P(x)y=Q(x)yn
is called a Bernoulli differential equation where n is any real number and n≠0 and n≠1.[56] It is named after Jacob Bernoulli who discussed it in 1695. Bernoulli equations are special because they are nonlinear differential equations with known exact solutions. A famous special case of the Bernoulli equation is the logistic differential equation.
Bernoulli's equation
An equation for relating several measurements within a fluid flow, such as velocity, pressure, and potential energy.
Bernoulli's principle
In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.[57]: Ch.3 [58]: 156–164, § 3.5 The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.[59] Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler who derived Bernoulli's equation in its usual form in 1752.[60][61] The principle is only applicable for isentropic flows: when the effects of irreversible processes (like turbulence) and non-adiabatic processes (e.g. heat radiation) are small and can be neglected.
Beta particle
also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β− decay and β+ decay, which produce electrons and positrons respectively.[62]
Binomial distribution
In probability theory and statistics, the binomial distribution with parameters n and p is the discrete probability distribution of the number of successes in a sequence of n independent experiments, each asking a yes–no question, and each with its own boolean-valued outcome: a random variable containing a single bit of information: success/yes/true/one (with probability p) or failure/no/false/zero (with probability q = 1 − p). A single success/failure experiment is also called a Bernoulli trial or Bernoulli experiment and a sequence of outcomes is called a Bernoulli process; for a single trial, i.e., n = 1, the binomial distribution is a Bernoulli distribution. The binomial distribution is the basis for the popular binomial test of statistical significance.
Biomedical engineering
Biomedical Engineering (BME) or Medical Engineering is the application of engineering principles and design concepts to medicine and biology for healthcare purposes (e.g. diagnostic or therapeutic). This field seeks to close the gap between engineering and medicine, combining the design and problem solving skills of engineering with medical biological sciences to advance health care treatment, including diagnosis, monitoring, and therapy.[63]
Biomimetic
Biomimetics or biomimicry is the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems.[64]
Bionics
The application of biological methods to engineering systems.
Biophysics
Is an interdisciplinary science that applies approaches and methods traditionally used in physics to study biological phenomena.[65][66][67] Biophysics covers all scales of biological organization, from molecular to organismic and populations. Biophysical research shares significant overlap with biochemistry, molecular biology, physical chemistry, physiology, nanotechnology, bioengineering, computational biology, biomechanics and systems biology.
Biot number
The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It is named after the eighteenth century French physicist Jean-Baptiste Biot (1774–1862), and gives a simple index of the ratio of the heat transfer resistances inside of and at the surface of a body. This ratio determines whether or not the temperatures inside a body will vary significantly in space, while the body heats or cools over time, from a thermal gradient applied to its surface.
Block and tackle
A system of pulleys and a rope threaded between them, used to lift or pull heavy loads.
Body force
Is a force that acts throughout the volume of a body. Forces due to gravity, electric fields and magnetic fields are examples of body forces. Body forces contrast with contact forces or surface forces which are exerted to the surface of an object.
Boiler
Is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications,[68][69] including water heating, central heating, boiler-based power generation, cooking, and sanitation.
Boiling point
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid[70][71] and the liquid changes into a vapor.
Boiling-point elevation
Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water. The boiling point can be measured accurately using an ebullioscope.
Boltzmann constant
The Boltzmann constant (kB or k) is a physical constant relating the average kinetic energy of particles in a gas with the temperature of the gas[72] and occurs in Planck's law of black-body radiation and in Boltzmann's entropy formula. It was introduced by Max Planck, but named after Ludwig Boltzmann. It is the gas constant R divided by the Avogadro constant NA:

k=RNA..
Boson
In quantum mechanics, a boson (/ˈboʊsɒn/,[73] /ˈboʊzɒn/[74]) is a particle that follows Bose–Einstein statistics. Bosons make up one of the two classes of particles, the other being fermions.[75] The name boson was coined by Paul Dirac[76][77] to commemorate the contribution of Indian physicist and professor of physics at University of Calcutta and at University of Dhaka, Satyendra Nath Bose[78][79] in developing, with Albert Einstein, Bose–Einstein statistics—which theorizes the characteristics of elementary particles.[80]
Boyle's law
Boyle's law (sometimes referred to as the Boyle–Mariotte law, or Mariotte's law[81]) is an experimental gas law that describes how the pressure of a gas tends to increase as the volume of the container decreases. A modern statement of Boyle's law is: The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.[82][83]
Bravais lattice
In geometry and crystallography, a Bravais lattice, named after Auguste Bravais (1850),[84] is an infinite array (or a finite array, if we consider the edges, obviously) of discrete points generated by a set of discrete translation operations described in three dimensional space by:

𝐑=n1𝐚1+n2𝐚2+n3𝐚3
where ni are any integers and ai are known as the primitive vectors which lie in different directions (not necessarily mutually perpendicular) and span the lattice. This discrete set of vectors must be closed under vector addition and subtraction. For any choice of position vector R, the lattice looks exactly the same.
Brayton cycle
A thermodynamic cycle model for an ideal heat engine, in which heat is added or removed at constant pressure; approximated by a gas turbine.
Break-even
The break-even point (BEP) in economics, business—and specifically cost accounting—is the point at which total cost and total revenue are equal, i.e. "even". There is no net loss or gain, and one has "broken even", though opportunity costs have been paid and capital has received the risk-adjusted, expected return. In short, all costs that must be paid are paid, and there is neither profit nor loss.[85][86]
Brewster's angle
Brewster's angle (also known as the polarization angle) is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized. This special angle of incidence is named after the Scottish physicist Sir David Brewster (1781–1868).[87][88]
Brittleness
A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses (which do not deform plastically) and some polymers, such as PMMA and polystyrene. Many steels become brittle at low temperatures (see ductile-brittle transition temperature), depending on their composition and processing.
Bromide
Any chemical substance made up of Bromine, along with other elements.
Brønsted–Lowry acid–base theory
Is an acid–base reaction theory which was proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923.[89][90] The fundamental concept of this theory is that when an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton (the hydrogen cation, or H+). This theory is a generalization of the Arrhenius theory.
Brownian motion
Brownian motion or pedesis is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the fast-moving molecules in the fluid.[91]
Buckingham π theorem
A method for determining ∏ groups, or dimensionless descriptors of physical phenomena.
Buffer solution
A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many systems that use buffering for pH regulation.
Bulk modulus
The bulk modulus (K or B) of a substance is a measure of how resistant to compression that substance is. It is defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume.[92] Other moduli describe the material's response (strain) to other kinds of stress: the shear modulus describes the response to shear, and Young's modulus describes the response to linear stress. For a fluid, only the bulk modulus is meaningful. For a complex anisotropic solid such as wood or paper, these three moduli do not contain enough information to describe its behaviour, and one must use the full generalized Hooke's law.
Buoyancy
A force caused by displacement in a fluid by an object of different density than the fluid.

## C

Calculus
The mathematics of change.
Capacitance
The ability of a body to store electrical charge.
Capacitive reactance
The impedance of a capacitor in an alternating current circuit, the opposition to current flow.
Capacitor
An electrical component that stores energy in an electric field.
Capillary action
Capillary action (sometimes capillarity, capillary motion, capillary effect, or wicking) is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid.[93]
Carbonate
Any mineral with bound carbon dioxide.
Carnot cycle
A hypothetical thermodynamic cycle for a heat engine; no thermodynamic cycle can be more efficient than a Carnot cycle operating between the same two temperature limits.
Cartesian coordinates
Coordinates within a rectangular Cartesian plane.
Castigliano's method
Named for Carlo Alberto Castigliano, is a method for determining the displacements of a linear-elastic system based on the partial derivatives of the energy. He is known for his two theorems. The basic concept may be easy to understand by recalling that a change in energy is equal to the causing force times the resulting displacement. Therefore, the causing force is equal to the change in energy divided by the resulting displacement. Alternatively, the resulting displacement is equal to the change in energy divided by the causing force. Partial derivatives are needed to relate causing forces and resulting displacements to the change in energy.
Casting
Forming of an object by pouring molten metal (or other substances) into a mold.
Cathode
The terminal of a device by which current exits.
Cathode ray
The stream of electrons emitted from a heated negative electrode and attracted to a positive electrode.
Cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates the interior of all cells from the outside environment (the extracellular space) which protects the cell from its environment[94][95] consisting of a lipid bilayer with embedded proteins.
Cell nucleus
In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, meaning kernel or seed) is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.
Cell theory
In biology, cell theory is the historic scientific theory, now universally accepted, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. Cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
Center of gravity
The center of mass of an object, its balance point.
Center of mass
The weighted center of an object; a force applied through the center of mass will not cause rotation of the object.
Center of pressure
Is the point where the total sum of a pressure field acts on a body, causing a force to act through that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure location produce equivalent force and moment on the body as the original pressure field.
Central force motion

Central limit theorem
In probability theory, the central limit theorem (CLT) establishes that, in some situations, when independent random variables are added, their properly normalized sum tends toward a normal distribution (informally a "bell curve") even if the original variables themselves are not normally distributed. The theorem is a key concept in probability theory because it implies that probabilistic and statistical methods that work for normal distributions can be applicable to many problems involving other types of distributions.
Central processing unit
A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling and input/output (I/O) operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s.[96] Traditionally, the term "CPU" refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.[97]
Centripetal acceleration

Centripetal force
A force acting against rotational acceleration.
Centroid
The average point of volume for an object.
Centrosome
In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression. The centrosome is thought to have evolved only in the metazoan lineage of eukaryotic cells.[98] Fungi and plants lack centrosomes and therefore use structures other than MTOCs to organize their microtubules.[99][100]
Chain reaction
Is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events.
Change of base rule

Charles's law
Charles's law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles's law is: When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be in direct proportion.[101]
Chemical bond
Is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are "strong bonds" or "primary bonds" such as covalent, ionic and metallic bonds, and "weak bonds" or "secondary bonds" such as dipole–dipole interactions, the London dispersion force and hydrogen bonding.
Chemical compound
Is a chemical substance composed of many identical molecules (or molecular entities) composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved.
Chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system.[102] Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal. Thus, there are no net changes in the concentrations of the reactant(s) and product(s). Such a state is known as dynamic equilibrium.[103][104]
Chemical kinetics
Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that can describe the characteristics of a chemical reaction.
Chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another.[105] Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
Chemistry
Is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.[106][107][108][109]
Chloride
Any chemical compound containing the element chlorine.
Chromate
Chromate salts contain the chromate anion, CrO2−4. Dichromate salts contain the dichromate anion, Cr2O2−7. They are oxoanions of chromium in the 6+ oxidation state . They are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.
Circular motion
In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations of motion describe the movement of the center of mass of a body.
Civil engineering
The profession that deals with the design and construction of structures, or other fixed works.
Clausius–Clapeyron relation
The Clausius–Clapeyron relation, named after Rudolf Clausius[110] and Benoît Paul Émile Clapeyron,[111] is a way of characterizing a discontinuous phase transition between two phases of matter of a single constituent. On a pressure–temperature (P–T) diagram, the line separating the two phases is known as the coexistence curve. The Clausius–Clapeyron relation gives the slope of the tangents to this curve. Mathematically,

dPdT=LTΔv=ΔsΔv,
where dP/dT is the slope of the tangent to the coexistence curve at any point, L is the specific latent heat, T is the temperature, Δv is the specific volume change of the phase transition, and Δs is the specific entropy change of the phase transition.
Clausius inequality

Clausius theorem
The Clausius theorem (1855) states that a system exchanging heat with external reservoirs and undergoing a cyclic process, is one that ultimately returns a system to its original state,

∮δQTsurr≤0,
where δQ is the infinitesimal amount of heat absorbed by the system from the reservoir and Tsurr is the temperature of the external reservoir (surroundings) at a particular instant in time. In the special case of a reversible process, the equality holds.[112] The reversible case is used to introduce the entropy state function. This is because in a cyclic process the variation of a state function is zero. In words, the Clausius statement states that it is impossible to construct a device whose sole effect is the transfer of heat from a cool reservoir to a hot reservoir.[113] Equivalently, heat spontaneously flows from a hot body to a cooler one, not the other way around.[114] The generalized "inequality of Clausius"[115]

dS>δQTsurr
for an infinitesimal change in entropy S applies not only to cyclic processes, but to any process that occurs in a closed system.
Coefficient of performance
The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required.[116][117] Higher COPs equate to lower operating costs. The COP usually exceeds 1, especially in heat pumps, because, instead of just converting work to heat (which, if 100% efficient, would be a COP_hp of 1), it pumps additional heat from a heat source to where the heat is required. For complete systems, COP calculations should include energy consumption of all power consuming auxiliaries. COP is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.[118]
Coefficient of variation
In probability theory and statistics, the coefficient of variation (CV), also known as relative standard deviation (RSD), is a standardized measure of dispersion of a probability distribution or frequency distribution. It is often expressed as a percentage, and is defined as the ratio of the standard deviation σ to the mean μ (or its absolute value, |μ|).
Coherence
In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. Coherence is an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets.
Cohesion
Or cohesive attraction or cohesive force is the action or property of like molecules sticking together, being mutually attractive. It is an intrinsic property of a substance that is caused by the shape and structure of its molecules, which makes the distribution of orbiting electrons irregular when molecules get close to one another, creating electrical attraction that can maintain a microscopic structure such as a water drop. In other words, cohesion allows for surface tension, creating a "solid-like" state upon which light-weight or low-density materials can be placed.
Cold forming
Or cold working, any metal-working procedure (such as hammering, rolling, shearing, bending, milling, etc.) carried out below the metal's recrystallization temperature.
Combustion
Or burning,[119] is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.
Compensation
Is planning for side effects or other unintended issues in a design. In a more simpler term, it's a "counter-procedure" plan on expected side effect performed to produce more efficient and useful results. The design of an invention can itself also be to compensate for some other existing issue or exception.
Compiler
A computer program that translates a high-level language into machine language.
Compressive strength
Compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size, as opposed to tensile strength, which withstands loads tending to elongate. In other words, compressive strength resists compression (being pushed together), whereas tensile strength resists tension (being pulled apart). In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.
Computational fluid dynamics
The numerical solution of flow equations in practical problems such as aircraft design or hydraulic structures.
Computer
A computer is a device that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of operations, called programs. These programs enable computers to perform an extremely wide range of tasks.
Computer-aided design
Computer-aided design (CAD) is the use of computer systems (or workstations) to aid in the creation, modification, analysis, or optimization of a design.[120] CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing.[121] CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. The term CADD (for Computer Aided Design and Drafting) is also used.[122]
Computer-aided engineering
Computer-aided engineering (CAE) is the broad usage of computer software to aid in engineering analysis tasks. It includes finite element analysis (FEA), computational fluid dynamics (CFD), multibody dynamics (MBD), durability and optimization.
Computer-aided manufacturing
Computer-aided manufacturing (CAM) is the use of software to control machine tools and related ones in the manufacturing of workpieces.[123][124][125][126][127] This is not the only definition for CAM, but it is the most common;[123] CAM may also refer to the use of a computer to assist in all operations of a manufacturing plant, including planning, management, transportation and storage.[128][129]
Computer engineering
Computer engineering is a discipline that integrates several fields of computer science and electronics engineering required to develop computer hardware and software.[130]
Computer science
Is the theory, experimentation, and engineering that form the basis for the design and use of computers. It involves the study of algorithms that process, store, and communicate digital information. A computer scientist specializes in the theory of computation and the design of computational systems.[131]
Concave lens
Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus.
Condensed matter physics
Is the field of physics that deals with the macroscopic and microscopic physical properties of matter. In particular it is concerned with the "condensed" phases that appear whenever the number of constituents in a system is extremely large and the interactions between the constituents are strong.
Confidence interval
In statistics, a confidence interval or compatibility interval (CI) is a type of interval estimate, computed from the statistics of the observed data, that might contain the true value of an unknown population parameter. The interval has an associated confidence level that, loosely speaking, quantifies the level of confidence that the parameter lies in the interval. More strictly speaking, the confidence level represents the frequency (i.e. the proportion) of possible confidence intervals that contain the true value of the unknown population parameter. In other words, if confidence intervals are constructed using a given confidence level from an infinite number of independent sample statistics, the proportion of those intervals that contain the true value of the parameter will be equal to the confidence level.[132][133][134]
Conjugate acid
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H+) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.[135] Because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic.
Conjugate base
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H+) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is what is left over after an acid has donated a proton during a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.[135] Because some acids are capable of releasing multiple protons, the conjugate base of an acid may itself be acidic.
Conservation of energy
In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time.[136] This law means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another.
Conservation of mass
The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system's mass cannot change, so quantity cannot be added nor removed. Hence, the quantity of mass is conserved over time.
Continuity equation
A continuity equation in physics is an equation that describes the transport of some quantity. It is particularly simple and powerful when applied to a conserved quantity, but it can be generalized to apply to any extensive quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved under their respective appropriate conditions, a variety of physical phenomena may be described using continuity equations.
Continuum mechanics
Is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such models in the 19th century.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Control engineering    Control engineering or control systems engineering is an engineering discipline that applies automatic control theory to design systems with desired behaviors in control environments.[137] The discipline of controls overlaps and is usually taught along with electrical engineering at many institutions around the world.[137] .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Convex lens    Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Corrosion    Is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Cosmic rays    Cosmic rays are high-energy radiation, mainly originating outside the Solar System.[138]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Coulomb    The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. It is the charge (symbol: Q or q) transported by a constant current of one ampere in one second:

1C=1A⋅1s
Thus, it is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:

1C=1F⋅1V
The coulomb is equivalent to the charge of approximately Lua error: Internal error: The interpreter has terminated with signal "24". (Lua error: Internal error: The interpreter has terminated with signal "24". mol) protons, and −1 C is equivalent to the charge of approximately Lua error: Internal error: The interpreter has terminated with signal "24". electrons. A new definition, in terms of the elementary charge, will take effect on 20 May 2019.[139] The new definition, defines the elementary charge (the charge of the proton) as exactly Lua error: Internal error: The interpreter has terminated with signal "24". coulombs. This would implicitly define the coulomb as ​1⁄Lua error: Internal error: The interpreter has terminated with signal "24".×10Lua error: Internal error: The interpreter has terminated with signal "24". elementary charges.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Coulomb's law    Coulomb's law, or Coulomb's inverse-square law, is a law of physics for quantifying Coulomb's force, or electrostatic force. Electrostatic force is the amount of force with which stationary, electrically charged particles either repel, or attract each other. This force and the law for quantifying it, represent one of the most basic forms of force used in the physical sciences, and were an essential basis to the study and development of the theory and field of classical electromagnetism. The law was first published in 1785 by French physicist Charles-Augustin de Coulomb.[140] In its scalar form, the law is:

F=keq1q2r2,
where ke is Coulomb's constant (ke ≈ Lua error: Internal error: The interpreter has terminated with signal "24".), q1 and q2 are the signed magnitudes of the charges, and the scalar r is the distance between the charges. The force of the interaction between the charges is attractive if the charges have opposite signs (i.e., F is negative) and repulsive if like-signed (i.e., F is positive). Being an inverse-square law, the law is analogous to Isaac Newton's inverse-square law of universal gravitation. Coulomb's law can be used to derive Gauss's law, and vice versa.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Covalent bond    A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Crookes tube    A type of vacuum tube that demonstrates cathode rays.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Cryogenics    The science of low temperatures.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Crystallization    Crystallization is the (natural or artificial) process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal. Some of the ways by which crystals form are precipitating from a solution, freezing, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Crystallography    The study of crystals.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Curvilinear motion    Describes the motion of a moving particle that conforms to a known or fixed curve. The study of such motion involves the use of two co-ordinate systems, the first being planar motion and the latter being cylindrical motion.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Cyclotron    A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929-1930 at the University of California, Berkeley,[141][142] and patented in 1932.[143][144] A cyclotron accelerates charged particles outwards from the center along a spiral path.[145][146] The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field. Lawrence was awarded the 1939 Nobel prize in physics for this invention.[146][147]

## D

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dalton's law    In chemistry and physics, Dalton's law (also called Dalton's law of partial pressures) states that in a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.[148]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Damped vibration    Any vibration with a force acting against it to lessen the vibration over time.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Darcy–Weisbach equation    An equation used in fluid mechanics to find the pressure change cause by friction within a pipe or conduit.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">DC motor    An electrical motor driven by direct current.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Decibel    A logarithmic unit of ratios.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Definite integral    The integral of a function between an upper and lower limit.[149]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Deflection    Is the degree to which a structural element is displaced under a load. It may refer to an angle or a distance.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Deformation (engineering)    In materials science, deformation refers to any changes in the shape or size of an object due to

* an applied force (the deformation energy in this case is transferred through work) or
* a change in temperature (the deformation energy in this case is transferred through heat).

The first case can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). In the second case, the most significant factor, which is determined by the temperature, is the mobility of the structural defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline solids. The movement or displacement of such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion.[150][151]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Deformation (mechanics)    Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration.[152] A configuration is a set containing the positions of all particles of the body. A deformation may be caused by external loads,[153] body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, etc.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Degrees of freedom    The number of parameters required to define the motion of a dynamical system.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Delta robot    A tripod linkage, used to construct fast-acting manipulators with a wide range of movement.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Delta-wye transformer    A type of transformer used in three-phase power systems.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">De Moivre–Laplace theorem    In probability theory, the de Moivre–Laplace theorem, which is a special case of the central limit theorem, states that the normal distribution may be used as an approximation to the binomial distribution under certain conditions. In particular, the theorem shows that the probability mass function of the random number of "successes" observed in a series of n independent Bernoulli trials, each having probability p of success (a binomial distribution with n trials), converges to the probability density function of the normal distribution with mean np and standard deviationnp(1−p), as n grows large, assuming p is not 0 or 1.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Density    The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:[154]

ρ=mV
where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume,[155] although this is scientifically inaccurate – this quantity is more specifically called specific weight.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Derivative    The derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. For example, the derivative of the position of a moving object with respect to time is the object's velocity: this measures how quickly the position of the object changes when time advances.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Design engineering    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dew point    The pressure and temperature at which air is holding the maximum possible humidity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Diamagnetism    Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted by a magnetic field. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material. The magnetic permeability of diamagnetic materials is less than μ0, the permeability of vacuum. In most materials diamagnetism is a weak effect which can only be detected by sensitive laboratory instruments, but a superconductor acts as a strong diamagnet because it repels a magnetic field entirely from its interior.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dielectric    An insulator, a material that does not permit free flow of electricity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Differential pressure    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Differential pulley    A differential pulley, also called Weston differential pulley, or colloquially chain fall, is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a continuous chain that wraps around pulleys. The relative size of two connected pulleys determines the maximum weight that can be lifted by hand. The load will remain in place (and not lower under the force of gravity) until the chain is pulled.[156]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Differential signaling    Is a method for electrically transmitting information using two complementary signals.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Diffusion    Is the net movement of molecules or atoms from a region of higher concentration (or high chemical potential) to a region of lower concentration (or low chemical potential).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dimensional analysis    is the analysis of the relationships between different physical quantities by identifying their base quantities (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms) and tracking these dimensions as calculations or comparisons are performed. The conversion of units from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the factor-label method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra.[157][158][159]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Direct integration of a beam    Direct integration is a structural analysis method for measuring internal shear, internal moment, rotation, and deflection of a beam. For a beam with an applied weight w(x), taking downward to be positive, the internal shear force is given by taking the negative integral of the weight:

V(x)=−∫w(x)dx
The internal moment M(x) is the integral of the internal shear:

M(x)=∫V(x)dx = −∫[∫w(x) dx]dx
The angle of rotation from the horizontal, θ, is the integral of the internal moment divided by the product of the Young's modulus and the area moment of inertia:

θ(x)=1EI∫M(x)dx
Integrating the angle of rotation obtains the vertical displacement ν:

ν(x)=∫θ(x)dx.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dispersion

In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency.[160] Media having this common property may be termed dispersive media. Sometimes the term chromatic dispersion is used for specificity. Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, in gravity waves (ocean waves), and for telecommunication signals along transmission lines (such as coaxial cable) or optical fiber.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Displacement (fluid)

In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this, the volume of the immersed object can be deduced (the volume of the immersed object will be exactly equal to the volume of the displaced fluid).

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Displacement (vector)

Is a vector whose length is the shortest distance from the initial to the final position of a point P.[161] It quantifies both the distance and direction of an imaginary motion along a straight line from the initial position to the final position of the point. A displacement may be identified with the translation that maps the initial position to the final position.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Distance

is a numerical measurement of how far apart objects are.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Doppler effect

The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.[162] It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dose–response relationship

The dose–response relationship, or exposure–response relationship, describes the magnitude of the response of an organism, as a function of exposure (or doses) to a stimulus or stressor (usually a chemical) after a certain exposure time.[163] Dose–response relationships can be described by dose–response curves. A stimulus response function or stimulus response curve is defined more broadly as the response from any type of stimulus, not limited to chemicals.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Drag

In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid.[164] This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity.[165][166] Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.[167] Drag forces always decrease fluid velocity relative to the solid object in the fluid's path.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Drift current

In condensed matter physics and electrochemistry, drift current is the electric current, or movement of charge carriers, which is due to the applied electric field, often stated as the electromotive force over a given distance. When an electric field is applied across a semiconductor material, a current is produced due to the flow of charge carriers.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ductility

Is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dynamics

Is the branch of classical mechanics concerned with the study of forces and their effects on motion. Isaac Newton defined the fundamental physical laws which govern dynamics in physics, especially his second law of motion.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Dyne

Is a derived unit of force specified in the centimetre–gram–second (CGS) system of units, a predecessor of the modern SI.

## E

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Economics    The scientific study of the production, distribution and consumption of goods.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Effusion    In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules.[168]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Elastic modulus    The amount a material will deform per unit force.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Elasticity    In physics, elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate forces are applied to them. If the material is elastic, the object will return to its initial shape and size when these forces are removed.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric charge    is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges; positive and negative (commonly carried by protons and electrons respectively). Like charges repel and unlike attract. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric circuit    Is an electrical network consisting of a closed loop, giving a return path for the current.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric current    Is a flow of electric charge.[169]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas (plasma).[170] The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter.[171]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric displacement field    In physics, the electric displacement field, denoted by D, is a vector field that appears in Maxwell's equations. It accounts for the effects of free and bound charge within materials. "D" stands for "displacement", as in the related concept of displacement current in dielectrics. In free space, the electric displacement field is equivalent to flux density, a concept that lends understanding to Gauss's law. In the International System of Units (SI), it is expressed in units of coulomb per meter squared (C⋅m−2).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric generator    In electricity generation, a generator,also called electric generator, electrical generator, and electromagnetic generator. is a device that converts motive power (mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbines, gas turbines, water turbines, internal combustion engines and even hand cranks.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric field    Surrounds an electric charge, and exerts force on other charges in the field, attracting or repelling them.[172][173] Electric field is sometimes abbreviated as E-field.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric field gradient    In atomic, molecular, and solid-state physics, the electric field gradient (EFG) measures the rate of change of the electric field at an atomic nucleus generated by the electronic charge distribution and the other nuclei.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric motor    Is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and winding currents to generate force in the form of rotation. Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators. An electric generator is mechanically identical to an electric motor, but operates in the reverse direction, accepting mechanical energy (such as from flowing water) and converting this mechanical energy into electrical energy.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric potential    (Also called the electric field potential, potential drop or the electrostatic potential) is the amount of work needed to move a unit of positive charge from a reference point to a specific point inside the field without producing an acceleration. Typically, the reference point is the Earth or a point at infinity, although any point beyond the influence of the electric field charge can be used.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical potential energy    Electric potential energy, or electrostatic potential energy, is a potential energy (measured in joules) that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system. An object may have electric potential energy by virtue of two key elements: its own electric charge and its relative position to other electrically charged objects. The term "electric potential energy" is used to describe the potential energy in systems with time-variant electric fields, while the term "electrostatic potential energy" is used to describe the potential energy in systems with time-invariant electric fields.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electric power    Is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical engineering    Is a technical discipline concerned with the study, design and application of equipment, devices and systems which use electricity, electronics, and electromagnetism. It emerged as an identified activity in the latter half of the 19th century after commercialization of the electric telegraph, the telephone, and electrical power generation, distribution and use. .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical conductance    The electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical conductor    Is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical impedance    Is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical insulator    Is a material whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical network    Is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources, current sources, resistances, inductances, capacitances). An electrical circuit is a network consisting of a closed loop, giving a return path for the current. Linear electrical networks, a special type consisting only of sources (voltage or current), linear lumped elements (resistors, capacitors, inductors), and linear distributed elements (transmission lines), have the property that signals are linearly superimposable. They are thus more easily analyzed, using powerful frequency domain methods such as Laplace transforms, to determine DC response, AC response, and transient response.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrical resistance    The electrical resistance of an object is a measure of its opposition to the flow of electric current. The inverse quantity is electrical conductance, and is the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with the notion of mechanical friction. The SI unit of electrical resistance is the ohm (Ω), while electrical conductance is measured in siemens (S).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electricity    Is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electrodynamics    In physics, the phenomena associated with moving electric charges, and their interaction with electric and magnetic fields; the study of these phenomena.[174]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electromagnet    Is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole, denoting the centre of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electromagnetic field    An electromagnetic field (also EM field) is a classical (i.e. non-quantum) field produced by accelerating electric charges.[175] It is the field described by classical electrodynamics and is the classical counterpart to the quantized electromagnetic field tensor in quantum electrodynamics. The electromagnetic field propagates at the speed of light (in fact, this field can be identified as light) and interacts with charges and currents. Its quantum counterpart is one of the four fundamental forces of nature (the others are gravitation, weak interaction and strong interaction.)
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electromagnetic radiation    In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy.[176] It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.[177]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electromechanics    Electromechanics[178][179][180][181] combines processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focuses on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each other. This process is especially prominent in systems such as those of DC or AC rotating electrical machines which can be designed and operated to generate power from a mechanical process (generator) or used to power a mechanical effect (motor). Electrical engineering in this context also encompasses electronics engineering.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electron    Is a subatomic particle, symbol e− or β−, whose electric charge is negative one elementary charge.[182] Electrons belong to the first generation of the lepton particle family,[183] and are generally thought to be elementary particles because they have no known components or substructure.[184] The electron has a mass that is approximately 1/1836 that of the proton.[185] Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.[183] Like all elementary particles, electrons exhibit properties of both particles and waves: they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer de Broglie wavelength for a given energy.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electronvolt    In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value Lua error: Internal error: The interpreter has terminated with signal "24". J.[186]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electron pair    In chemistry, an electron pair, or Lewis pair, consists of two electrons that occupy the same molecular orbital but have opposite spins. Gilbert N. Lewis introduced the concepts of both the electron pair and the covalent bond in a landmark paper he published in 1916.[187]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electronegativity    Symbolized as χ, is the measurement of the tendency of an atom to attract a shared pair of electrons (or electron density).[188] An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Electronics    Comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter.[189] It uses active devices to control electron flow by amplification and rectification, which distinguishes it from classical electrical engineering which uses passive effects such as resistance, capacitance and inductance to control current flow.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Endothermic process    Is any process with an increase in the enthalpy H (or internal energy U) of the system.[190] In such a process, a closed system usually absorbs thermal energy from its surroundings, which is heat transfer into the system. It may be a chemical process, such as dissolving ammonium nitrate in water, or a physical process, such as the melting of ice cubes.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Energy    In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.[note 1] Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Engine    An engine or motor is a machine designed to convert one form of energy into mechanical energy.[191][192] Heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a heat engine, in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Engineering    Is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings.[193] The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. The term engineering is derived from the Latin ingenium, meaning "cleverness" and ingeniare, meaning "to contrive, devise".[194]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Engineering economics    Engineering economics, previously known as engineering economy, is a subset of economics concerned with the use and "...application of economic principles"[195] in the analysis of engineering decisions.[196] As a discipline, it is focused on the branch of economics known as microeconomics in that it studies the behavior of individuals and firms in making decisions regarding the allocation of limited resources. Thus, it focuses on the decision making process, its context and environment.[195] It is pragmatic by nature, integrating economic theory with engineering practice.[195] But, it is also a simplified application of microeconomic theory in that it assumes elements such as price determination, competition and demand/supply to be fixed inputs from other sources.[195] As a discipline though, it is closely related to others such as statistics, mathematics and cost accounting.[195] It draws upon the logical framework of economics but adds to that the analytical power of mathematics and statistics.[195]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Engineering ethics    Is the field of system of moral principles that apply to the practice of engineering. The field examines and sets the obligations by engineers to society, to their clients, and to the profession. As a scholarly discipline, it is closely related to subjects such as the philosophy of science, the philosophy of engineering, and the ethics of technology.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Environmental engineering    Is a job type that is a professional engineering discipline and takes from broad scientific topics like chemistry, biology, ecology, geology, hydraulics, hydrology, microbiology, and mathematics to create solutions that will protect and also improve the health of living organisms and improve the quality of the environment.[197][198] Environmental engineering is a sub-discipline of civil engineering and chemical engineering.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Engineering physics    Or engineering science, refers to the study of the combined disciplines of physics, mathematics, chemistry, biology, and engineering, particularly computer, nuclear, electrical, electronic, aerospace, materials or mechanical engineering. By focusing on the scientific method as a rigorous basis, it seeks ways to apply, design, and develop new solutions in engineering.[199][200][201][202]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Enzyme    Enzymes are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. Almost all metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life.[203]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24".
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Escape velocity    The minimum velocity at which an object can escape a gravitation field.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Estimator    In statistics, an estimator is a rule for calculating an estimate of a given quantity based on observed data: thus the rule (the estimator), the quantity of interest (the estimand) and its result (the estimate) are distinguished.[204] For example, the sample mean is a commonly used estimator of the population mean. There are point and interval estimators. The point estimators yield single-valued results, although this includes the possibility of single vector-valued results and results that can be expressed as a single function. This is in contrast to an interval estimator, where the result would be a range of plausible values (or vectors or functions).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Euler–Bernoulli beam theory    Euler–Bernoulli beam theory (also known as engineer's beam theory or classical beam theory)[205] is a simplification of the linear theory of elasticity which provides a means of calculating the load-carrying and deflection characteristics of beams. It covers the case for small deflections of a beam that are subjected to lateral loads only. It is thus a special case of Timoshenko beam theory. It was first enunciated circa 1750,[206] but was not applied on a large scale until the development of the Eiffel Tower and the Ferris wheel in the late 19th century. Following these successful demonstrations, it quickly became a cornerstone of engineering and an enabler of the Second Industrial Revolution. Additional mathematical models have been developed such as plate theory, but the simplicity of beam theory makes it an important tool in the sciences, especially structural and mechanical engineering.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Exothermic process    In thermodynamics, the term exothermic process (exo- : "outside") describes a process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). Its etymology stems from the Greek prefix έξω (exō, which means "outwards") and the Greek word θερμικός (thermikόs, which means "thermal").[207]

## F

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Factor of safety    (FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Falling bodies    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Farad    [208] The farad (symbol: F) is the SI derived unit of electrical capacitance, the ability of a body to store an electrical charge. It is named after the English physicist Michael Faraday.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Faraday constant    Denoted by the symbol F and sometimes stylized as ℱ, is named after Michael Faraday. In physics and chemistry, this constant represents the magnitude of electric charge per mole of electrons.[209] It has the value

Lua error: Internal error: The interpreter has terminated with signal "24". C mol−1.[210]
This constant has a simple relation to two other physical constants:

F=eNA
where

e = Lua error: Internal error: The interpreter has terminated with signal "24".;[211]
NA = Lua error: Internal error: The interpreter has terminated with signal "24"..[212]
Both of these values have exact defined values, and hence F has a known exact value. NA is the Avogadro constant (the ratio of the number of particles, N, which is unitless, to the amount of substance, n, in units of moles), and e is the elementary charge or the magnitude of the charge of an electron. This relation holds because the amount of charge of a mole of electrons is equal to the amount of charge in one electron multiplied by the number of electrons in a mole.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fermat's principle    In optics, Fermat's principle, or the principle of least time, named after French mathematician Pierre de Fermat, is the principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. This principle is sometimes taken as the definition of a ray of light.[213] However, this version of the principle is not general; a more modern statement of the principle is that rays of light traverse the path of stationary optical length with respect to variations of the path.[214] In other words, a ray of light prefers the path such that there are other paths, arbitrarily nearby on either side, along which the ray would take almost exactly the same time to traverse.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fick's laws of diffusion    Describe diffusion and were derived by Adolf Fick in 1855. They can be used to solve for the diffusion coefficient, D. Fick's first law can be used to derive his second law which in turn is identical to the diffusion equation.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Finite element method    (FEM), is the most widely used method for solving problems of engineering and mathematical models. Typical problem areas of interest include the traditional fields of structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential. The FEM is a particular numerical method for solving partial differential equations in two or three space variables (i.e., some boundary value problems). To solve a problem, the FEM subdivides a large system into smaller, simpler parts that are called finite elements. This is achieved by a particular space discretization in the space dimensions, which is implemented by the construction of a mesh of the object: the numerical domain for the solution, which has a finite number of points. The finite element method formulation of a boundary value problem finally results in a system of algebraic equations. The method approximates the unknown function over the domain.[215] The simple equations that model these finite elements are then assembled into a larger system of equations that models the entire problem. The FEM then uses variational methods from the calculus of variations to approximate a solution by minimizing an associated error function.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">FIRST    For Inspiration and Recognition of Science and Technology – is an organization founded by inventor Dean Kamen in 1989 to develop ways to inspire students in engineering and technology fields.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fission    In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Flow velocity    In continuum mechanics the flow velocity in fluid dynamics, also macroscopic velocity[216][217] in statistical mechanics, or drift velocity in electromagnetism, is a vector field used to mathematically describe the motion of a continuum. The length of the flow velocity vector is the flow speed and is a scalar. It is also called velocity field; when evaluated along a line, it is called a velocity profile (as in, e.g., law of the wall).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fluid    In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases and plasmas. They are substances with zero shear modulus, or, in simpler terms, substances which cannot resist any shear force applied to them.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fluid dynamics    In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fluid mechanics    Is the branch of physics concerned with the mechanics of fluids (liquids, gases, and plasmas) and the forces on them.[218] It has applications in a wide range of disciplines, including mechanical, civil, chemical and biomedical engineering, geophysics, oceanography, meteorology, astrophysics, and biology.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fluid statics    Fluid statics, or hydrostatics, is the branch of fluid mechanics that studies "fluids at rest and the pressure in a fluid or exerted by a fluid on an immersed body".[219]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Flywheel    Is a mechanical device specifically designed to use the conservation of angular momentum so as to efficiently store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, if we assume the flywheel's moment of inertia to be constant (i.e., a flywheel with fixed mass and second moment of area revolving about some fixed axis) then the stored (rotational) energy is directly associated with the square of its rotational speed.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Focus    In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge.[220] Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Foot-pound    The foot-pound force (symbol: ft⋅lbf,[221] ft⋅lbf,[222] or ft⋅lb [223]) is a unit of work or energy in the engineering and gravitational systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of one foot. The corresponding SI unit is the joule.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fracture toughness    In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property. The critical value of stress intensity factor in mode I loading measured under plane strain conditions is known as the plane strain fracture toughness, denoted KIc.[224] When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is given the designation Kc. Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fraunhofer lines    In physics and optics, the Fraunhofer lines are a set of spectral absorption lines named after the German physicist Joseph von Fraunhofer (1787–1826). The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Free fall    In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on it.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Frequency modulation    Frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Freezing point    The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of substances to supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the melting point.[225]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Friction    Is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.[226] There are several types of friction:

* Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction ("stiction") between non-moving surfaces, and kinetic friction between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure 1).
* Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other.[227][228]

* Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces.[229][230][231]

* Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
* Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.[228]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Function    In mathematics, a function[note 2] is a binary relation between two sets that associates every element of the first set to exactly one element of the second set. Typical examples are functions from integers to integers, or from the real numbers to real numbers.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fundamental frequency    The fundamental frequency, often referred to simply as the fundamental, is defined as the lowest frequency of a periodic waveform. In music, the fundamental is the musical pitch of a note that is perceived as the lowest partial present. In terms of a superposition of sinusoids, the fundamental frequency is the lowest frequency sinusoidal in the sum of harmonically related frequencies, or the frequency of the difference between adjacent frequencies. In some contexts, the fundamental is usually abbreviated as f0, indicating the lowest frequency counting from zero.[232][233][234] In other contexts, it is more common to abbreviate it as f1, the first harmonic.[235][236][237][238][239] (The second harmonic is then f2 = 2⋅f1, etc. In this context, the zeroth harmonic would be 0 Hz.)
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fundamental interaction    In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four fundamental interactions known to exist: the gravitational and electromagnetic interactions, which produce significant long-range forces whose effects can be seen directly in everyday life, and the strong and weak interactions, which produce forces at minuscule, subatomic distances and govern nuclear interactions. Some scientists hypothesize that a fifth force might exist, but these hypotheses remain speculative.[240][241][242]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fundamental theorem of calculus    Is a theorem that links the concept of differentiating a function with the concept of integrating a function.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Fundamentals of Engineering Examination (US)    The Fundamentals of Engineering (FE) exam, also referred to as the Engineer in Training (EIT) exam, and formerly in some states as the Engineering Intern (EI) exam, is the first of two examinations that engineers must pass in order to be licensed as a Professional Engineer in the United States . The second examination is Principles and Practice of Engineering Examination. The FE exam is open to anyone with a degree in engineering or a related field, or currently enrolled in the last year of an ABET-accredited engineering degree program. Some state licensure boards permit students to take it prior to their final year, and numerous states allow those who have never attended an approved program to take the exam if they have a state-determined number of years of work experience in engineering. Some states allow those with ABET-accredited "Engineering Technology" or "ETAC" degrees to take the examination. The state of Michigan has no admission pre-requisites for the FE.[243] The exam is administered by the National Council of Examiners for Engineering and Surveying (NCEES).

## G

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Galvanic cell    A galvanic cell or voltaic cell, named after Luigi Galvani or Alessandro Volta, respectively, is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell. It generally consists of two different metals immersed in electrolytes, or of individual half-cells with different metals and their ions in solution connected by a salt bridge or separated by a porous membrane. Volta was the inventor of the voltaic pile, the first electrical battery. In common usage, the word "battery" has come to include a single galvanic cell, but a battery properly consists of multiple cells.[244]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gamma rays    A gamma ray, or gamma radiation (symbol γ or γ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gas    Is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compound molecules made from a variety of atoms (e.g. carbon dioxide). A gas mixture, such as air, contains a variety of pure gases. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gauge pressure    Is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Geiger counter    Is an instrument used for detecting and measuring ionizing radiation. Also known as a Geiger–Muller counter (or Geiger–Müller counter), it is widely used in applications such as radiation dosimetry, radiological protection, experimental physics, and the nuclear industry.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">General relativity    General relativity, also known as the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Geometric mean    In mathematics, the geometric mean is a mean or average, which indicates the central tendency or typical value of a set of numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum). The geometric mean is defined as the nth root of the product of n numbers, i.e., for a set of numbers x1, x2, ..., xn, the geometric mean is defined as

(∏i=1nxi)1n=x1x2⋯xnn

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Geometry

Is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space that are related with distance, shape, size, and relative position of figures.[245] A mathematician who works in the field of geometry is called a geometer.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Geophysics

Is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term geophysics sometimes refers only to geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation.[246] However, modern geophysics organizations and pure scientists use a broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial relations; and analogous problems associated with the Moon and other planets.[246][247][248][249][250]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Geotechnical engineering

Also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles and methods of soil mechanics and rock mechanics for the solution of engineering problems and the design of engineering works. It also relies on knowledge of geology, hydrology, geophysics, and other related sciences.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gluon

Is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles.[251] In layman's terms, they "glue" quarks together, forming hadrons such as protons and neutrons. In technical terms, gluons are vector gauge bosons that mediate strong interactions of quarks in quantum chromodynamics (QCD). Gluons themselves carry the color charge of the strong interaction. This is unlike the photon, which mediates the electromagnetic interaction but lacks an electric charge. Gluons therefore participate in the strong interaction in addition to mediating it, making QCD significantly harder to analyze than quantum electrodynamics (QED).

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Graham's law

Graham's law of effusion (also called Graham's law of diffusion) was formulated by Scottish physical chemist Thomas Graham in 1848.[252] Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles.[252] This formula can be written as:

Rate1Rate2=M2M1,
where:

Rate1 is the rate of effusion for the first gas. (volume or number of moles per unit time).
Rate2 is the rate of effusion for the second gas.

M1 is the molar mass of gas 1
M2 is the molar mass of gas 2.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravitational constant

The gravitational constant (also known as the universal gravitational constant, the Newtonian constant of gravitation, or the Cavendish gravitational constant),[lower-alpha 1] denoted by the letter G, is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general theory of relativity.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravitational energy

Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (converted into kinetic energy) when the objects fall towards each other. Gravitational potential energy increases when two objects are brought further apart. For two pairwise interacting point particles, the gravitational potential energy U is given by

U=−GMmR,
where M and m are the masses of the two particles, R is the distance between them, and G is the gravitational constant.[253] Close to the Earth's surface, the gravitational field is approximately constant, and the gravitational potential energy of an object reduces to

U=mgh
where m is the object's mass, g=GME/RE2 is the gravity of Earth, and h is the height of the object's center of mass above a chosen reference level.[253]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravitational field

In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body.[254] Thus, a gravitational field is used to explain gravitational phenomena, and is measured in newtons per kilogram (N/kg). In its original concept, gravity was a force between point masses. Following Isaac Newton, Pierre-Simon Laplace attempted to model gravity as some kind of radiation field or fluid, and since the 19th century, explanations for gravity have usually been taught in terms of a field model, rather than a point attraction. In a field model, rather than two particles attracting each other, the particles distort spacetime via their mass, and this distortion is what is perceived and measured as a "force".Lua error: Internal error: The interpreter has terminated with signal "24". In such a model one states that matter moves in certain ways in response to the curvature of spacetime,[255] and that there is either no gravitational force,[256] or that gravity is a fictitious force.[257] Gravity is distinguished from other forces by its obedience to the equivalence principle.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravitational potential

In classical mechanics, the gravitational potential at a location is equal to the work (energy transferred) per unit mass that would be needed to move an object to that location from a fixed reference location. It is analogous to the electric potential with mass playing the role of charge. The reference location, where the potential is zero, is by convention infinitely far away from any mass, resulting in a negative potential at any finite distance. In mathematics, the gravitational potential is also known as the Newtonian potential and is fundamental in the study of potential theory. It may also be used for solving the electrostatic and magnetostatic fields generated by uniformly charged or polarized ellipsoidal bodies.[258]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravitational wave

Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light. They were proposed by Henri Poincaré in 1905[259] and subsequently predicted in 1916[260][261] by Albert Einstein on the basis of his general theory of relativity.[262][263] Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation.[264] Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate instantaneously (at infinite speed) - showing one of the ways the methods of classical physics are unable to explain phenomena associated with relativity.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Gravity

Or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light[265]—are brought toward (or gravitate toward) one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing and forming stars and caused the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become increasingly weaker as objects get further away.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ground state

The ground state of a quantum-mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In quantum field theory, the ground state is usually called the vacuum state or the vacuum.

## H

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Half-life    The period at which one-half of a quantity of an unstable isotope has decayed into other elements; the time at which half of a substance has diffused out of or otherwise reacted in a system.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Haptic    Tactile feedback technology using the operator's sense of touch. Also sometimes applied to robot manipulators with their own touch sensitivity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hardness    Is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. Some materials (e.g. metals) are harder than others (e.g. plastics, wood). Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore, there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness. Hardness is dependent on ductility, elastic stiffness, plasticity, strain, strength, toughness, viscoelasticity, and viscosity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Harmonic mean    In mathematics, the harmonic mean (sometimes called the subcontrary mean) is one of several kinds of average, and in particular, one of the Pythagorean means. Typically, it is appropriate for situations when the average of rates is desired. The harmonic mean can be expressed as the reciprocal of the arithmetic mean of the reciprocals of the given set of observations. As a simple example, the harmonic mean of 1, 4, and 4 is

(1−1+4−1+4−13)−1=311+14+14=31.5=2.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Heat

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.[266][267][268][269][270][271][272]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Heat transfer

Is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Helmholtz free energy

In thermodynamics, the Helmholtz free energy (or Helmholtz energy) is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature and volume (isothermal, isochoric). The negative of the change in the Helmholtz energy during a process is equal to the maximum amount of work that the system can perform in a thermodynamic process in which volume is held constant. If the volume were not held constant, part of this work would be performed as boundary work. This makes the Helmholtz energy useful for systems held at constant volume. Furthermore, at constant temperature, the Helmholtz free energy is minimized at equilibrium.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Henderson–Hasselbalch equation

In chemistry and biochemistry, the Henderson–Hasselbalch equation

pH=pKa+log10([Base][Acid])
can be used to estimate the pH of a buffer solution. The numerical value of the acid dissociation constant, Ka, of the acid is known or assumed. The pH is calculated for given values of the concentrations of the acid, HA and of a salt, MA, of its conjugate base, A−; for example, the solution may contain acetic acid and sodium acetate.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Henry's law

In physical chemistry, Henry's law is a gas law that states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid. The proportionality factor is called Henry's law constant. It was formulated by the English chemist William Henry, who studied the topic in the early 19th century.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hertz

The SI unit of frequency, one cycle per second.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hexapod

(platform) – a movable platform using six linear actuators. Often used in flight simulators they also have applications as a robotic manipulator.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hexapod

(walker) – a six-legged walking robot, using a simple insect-like locomotion.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hoist

Is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting medium. The most familiar form is an elevator, the car of which is raised and lowered by a hoist mechanism. Most hoists couple to their loads using a lifting hook. Today, there are a few governing bodies for the North American overhead hoist industry which include the Hoist Manufactures Institute (HMI), ASME, and the Occupational Safety and Health Administration (OSHA). HMI is a product counsel of the Material Handling Industry of America consisting of hoist manufacturers promoting safe use of their products.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Horsepower

In measurement systems that use feet, the unit of power.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hot working

Or hot forming, any metal-working procedure (such as forging, rolling, extruding, etc.) carried out above the metal's recrystallization temperature.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Huygens–Fresnel principle

The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and France physicist Augustin-Jean Fresnel) is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction and also reflection. It states that every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere.[273] The sum of these spherical wavelets forms the wavefront.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hydraulics

The study of fluid flow, or the generation of mechanical force and movement by liquid under pressure.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Hydrocarbon

A compound containing hydrogen and carbon atoms only; petroleum is made of hydrocarbons.

## I

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ice point    The freezing point of pure water at one atmosphere; 0°C (32°F).[274]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ideal gas    A model for gases that ignores inter-molecular forces. Most gases are approximately ideal at some high temperature and low pressure.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ideal gas constant    The constant in the gas law that relates pressure, volume and temperature.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ideal gas law    Also called the general gas equation, is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions, although it has several limitations. It was first stated by Benoît Paul Émile Clapeyron in 1834 as a combination of the empirical Boyle's law, Charles's law, Avogadro's law, and Gay-Lussac's law.[275] The ideal gas law is often written in an empirical form:

PV=nRT
where P, V and T are the pressure, volume and temperature; n is the amount of substance; and R is the ideal gas constant. It is the same for all gases. It can also be derived from the microscopic kinetic theory, as was achieved (apparently independently) by August Krönig in 1856[276] and Rudolf Clausius in 1857.[277]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Identity    In mathematics, an identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B (which might contain some variables) produce the same value for all values of the variables within a certain range of validity.[278][279] In other words, A = B is an identity if A and B define the same functions, and an identity is an equality between functions that are differently defined. For example, (a+b)2=a2+2ab+b2 and cos2θ+sin2θ=1 are identities.[280] Identities are sometimes indicated by the triple bar symbol ≡ instead of =, the equals sign.[281]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Impedance (electrical)    In electrical engineering, electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Inclined plane    Also known as a ramp, is a flat supporting surface tilted at an angle, with one end higher than the other, used as an aid for raising or lowering a load.[282][283][284] The inclined plane is one of the six classical simple machines defined by Renaissance scientists. Inclined planes are widely used to move heavy loads over vertical obstacles; examples vary from a ramp used to load goods into a truck, to a person walking up a pedestrian ramp, to an automobile or railroad train climbing a grade.[284]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Indefinite integral    A function whose derivative is a given function; an antiderivative.[285]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Inductance    In electromagnetism and electronics, inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the current, and follows any changes in current. From Faraday's law of induction, any change in magnetic field through a circuit induces an electromotive force (EMF) (voltage) in the conductors, a process known as electromagnetic induction. This induced voltage created by the changing current has the effect of opposing the change in current. This is stated by Lenz's law, and the voltage is called back EMF. Inductance is defined as the ratio of the induced voltage to the rate of change of current causing it. It is a proportionality factor that depends on the geometry of circuit conductors and the magnetic permeability of nearby materials.[286] An electronic component designed to add inductance to a circuit is called an inductor. It typically consists of a coil or helix of wire.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Inductor    An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it.[287] An inductor typically consists of an insulated wire wound into a coil.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Industrial engineering    Is an engineering profession that is concerned with the optimization of complex processes, systems, or organizations by developing, improving and implementing integrated systems of people, money, knowledge, information and equipment. Industrial engineers use specialized knowledge and skills in the mathematical, physical and social sciences, together with the principles and methods of engineering analysis and design, to specify, predict, and evaluate the results obtained from systems and processes.[288] From these results, they are able to create new systems, processes or situations for the useful coordination of labour, materials and machines and also improve the quality and productivity of systems, physical or social.[289]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Inertia    Is the resistance of any physical object to any change in its velocity. This includes changes to the object's speed, or direction of motion. An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces act upon them.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Infrasound    Infrasound, sometimes referred to as low-frequency sound, describes sound waves with a frequency below the lower limit of audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing low sound, but at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Integral    In mathematics, an integral assigns numbers to functions in a way that describes displacement, area, volume, and other concepts that arise by combining infinitesimal data. The process of finding integrals is called integration. Along with differentiation, integration is a fundamental operation of calculus,[lower-alpha 2] and serves as a tool to solve problems in mathematics and physics involving the area of an arbitrary shape, the length of a curve, and the volume of a solid, among others.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Integral transform    In mathematics, an integral transform maps a function from its original function space into another function space via integration, where some of the properties of the original function might be more easily characterized and manipulated than in the original function space. The transformed function can generally be mapped back to the original function space using the inverse transform.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">International System of Units    The International System of Units (SI, abbreviated from the French Lua error: Internal error: The interpreter has terminated with signal "24".) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second (the unit of time with the symbol s), metre (length, m), kilogram (mass, kg), ampere (electric current, A), kelvin (thermodynamic temperature, K), mole (amount of substance, mol), and candela (luminous intensity, cd). The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units.[Note 1] Twenty-two derived units have been provided with special names and symbols.[Note 2] The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units,[Note 3] which are adopted to facilitate measurement of diverse quantities. The SI system also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten (i.e. decimal) multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Interval estimation    In statistics, interval estimation is the use of sample data to calculate an interval of possible values of an unknown population parameter; this is in contrast to point estimation, which gives a single value. Jerzy Neyman (1937) identified interval estimation ("estimation by interval") as distinct from point estimation ("estimation by unique estimate"). In doing so, he recognized that then-recent work quoting results in the form of an estimate plus-or-minus a standard deviation indicated that interval estimation was actually the problem statisticians really had in mind.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Inorganic chemistry    Deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disciplines is far from absolute, as there is much overlap in the subdiscipline of organometallic chemistry. It has applications in every aspect of the chemical industry, including catalysis, materials science, pigments, surfactants, coatings, medications, fuels, and agriculture.[290]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ion    Is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convention. The net charge of an ion is non-zero due to its total number of electrons being unequal to its total number of protons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ionic bonding    Is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities,[291] and is the primary interaction occurring in ionic compounds. It is one of the main types of bonding along with covalent bonding and metallic bonding. Ions are atoms (or groups of atoms) with an electrostatic charge. Atoms that gain electrons make negatively charged ions (called anions). Atoms that lose electrons make positively charged ions (called cations). This transfer of electrons is known as electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be of a more complex nature, e.g. molecular ions like NH+4 or SO2−4. In simpler words, an ionic bond results from the transfer of electrons from a metal to a non-metal in order to obtain a full valence shell for both atoms.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ionization    Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Isotope    Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.[292]

## J

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">J/psi meson    The J/ψ (J/psi) meson Lua error: Internal error: The interpreter has terminated with signal "24". or psion[293] is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium". The J/ψ is the most common form of charmonium, due to its spin of 1 and its low rest mass. The J/ψ has a rest mass of Lua error: Internal error: The interpreter has terminated with signal "24"., just above that of the ηc (Lua error: Internal error: The interpreter has terminated with signal "24".), and a mean lifetime of Lua error: Internal error: The interpreter has terminated with signal "24".. This lifetime was about a thousand times longer than expected.[294]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Joule    The SI unit of energy.The joule, (symbol: J), is a derived unit of energy in the International System of Units.[295] It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).[296][297][298] gh a conductor produces heat.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Joule heating    Also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat.

## K

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Kalman filter    In statistics and control theory, Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, containing statistical noise and other inaccuracies, and produces estimates of unknown variables that tend to be more accurate than those based on a single measurement alone, by estimating a joint probability distribution over the variables for each timeframe. The Kalman filter has numerous applications in technology.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Kelvin    Is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. The kelvin (symbol: K) is the base unit of temperature in the International System of Units (SI).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Kelvin–Planck statement    (Or the Heat Engine Statement), of the second law of thermodynamics states that it is impossible to devise a cyclically operating heat engine, the effect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.[299] This implies that it is impossible to build a heat engine that has 100% thermal efficiency.[300]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Kinematics    Is a branch of classical mechanics that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that caused the motion.[301][302][303]

## L

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Laminar flow    In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing.[304] At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids.[305] In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface.[306] Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Laplace transform    In mathematics, the Laplace transform, named after its inventor Pierre-Simon Laplace (Lua error: Internal error: The interpreter has terminated with signal "24".), is an integral transform that converts a function of a real variable t (often time) to a function of a complex variable s (complex frequency). The transform has many applications in science and engineering because it is a tool for solving differential equations. In particular, it transforms differential equations into algebraic equations and convolution into multiplication.[307][308][309]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">LC circuit    A circuit consisting entirely of inductors (L) and capacitors (C).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Le Chatelier's principle    Le Chatelier's principle, also called Chatelier's principle, is a principle of chemistry used to predict the effect of a change in conditions on chemical equilibria. The principle is named after French chemist Henry Louis Le Chatelier, and sometimes also credited to Karl Ferdinand Braun, who discovered it independently. It can be stated as:

> When any system at equilibrium for a long period of time is subjected to a change in concentration, temperature, volume, or pressure, (1) the system changes to a new equilibrium, and (2) this change partly counteracts the applied change.

It is common to treat the principle as a more general observation of systems,[310] such as

> When a settled system is disturbed, it will adjust to diminish the change that has been made to it

or, "roughly stated",[310]

> Any change in status quo prompts an opposing reaction in the responding system.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Lenz's law    Lenz's law, named after the physicist Emil Lenz who formulated it in 1834,[311] states that the direction of the electric current which is induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes the initial changing magnetic field. It is a qualitative law that specifies the direction of induced current, but states nothing about its magnitude. Lenz's law explains the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or the drag force of eddy currents exerted on moving objects in a magnetic field. Lenz's law may be seen as analogous to Newton's third law in classical mechanics.[312]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Lepton    In particle physics, a lepton is an elementary particle of half-integer spin (spin ​1⁄2) that does not undergo strong interactions.[313] Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the electron.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Lever    Is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or fulcrum. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is divided into three types. Also, leverage is mechanical advantage gained in a system. It is one of the six simple machines identified by Renaissance scientists. A lever amplifies an input force to provide a greater output force, which is said to provide leverage. The ratio of the output force to the input force is the mechanical advantage of the lever. As such, the lever is a mechanical advantage device, trading off force against movement.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">L'Hôpital's rule    In mathematics, more specifically calculus, L'Hôpital's rule or L'Hospital's rule (French: [lopital], Lua error: Internal error: The interpreter has terminated with signal "24"., Lua error: Internal error: The interpreter has terminated with signal "24".) provides a technique to evaluate limits of indeterminate forms. Application (or repeated application) of the rule often converts an indeterminate form to an expression that can be easily evaluated by substitution. The rule is named after the 17th-century France mathematician Guillaume de l'Hôpital. Although the rule is often attributed to L'Hôpital, the theorem was first introduced to him in 1694 by the Swiss mathematician Johann Bernoulli. L'Hôpital's rule states that for functions f and g which are differentiable on an open interval I except possibly at a point c contained in I, if limx->cf(x)=limx->cg(x)=0 or ±∞, and g′(x)≠0 for all x in I with x ≠ c, and limx->cf′(x)g′(x) exists, then

limx->cf(x)g(x)=limx->cf′(x)g′(x).
The differentiation of the numerator and denominator often simplifies the quotient or converts it to a limit that can be evaluated directly.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Light    Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye.[314] Visible light is usually defined as having wavelengths in the range of 400–700 nm, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).[315][316] This wavelength means a frequency range of roughly 430–750 terahertz (THz).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Linear actuator    Is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as disk drives and printers, in valves and dampers, and in many other places where linear motion is required. Hydraulic or pneumatic cylinders inherently produce linear motion. Many other mechanisms are used to generate linear motion from a rotating motor.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Linear algebra    The mathematics of equations where the unknowns are only in the first power.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Linear elasticity    Is a mathematical model of how solid objects deform and become internally stressed due to prescribed loading conditions. It is a simplification of the more general nonlinear theory of elasticity and a branch of continuum mechanics.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Liquid    A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, and plasma), and is the only state with a definite volume but no fixed shape. A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds. Like a gas, a liquid is able to flow and take the shape of a container. Most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, leading to wetting phenomena. Water is, by far, the most common liquid on Earth.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Logarithm    In mathematics, the logarithm is the inverse function to exponentiation. That means the logarithm of a given number x is the exponent to which another fixed number, the base b, must be raised, to produce that number x. In the simplest case, the logarithm counts the number of occurrences of the same factor in repeated multiplication; e.g., since 1000 = 10 × 10 × 10 = 103, the "logarithm base 10" of 1000 is 3, or log10(1000) = 3. The logarithm of x to base b is denoted as logb(x), or without parentheses, logb x, or even without the explicit base, log x, when no confusion is possible, or when the base does not matter such as in big O notation. More generally, exponentiation allows any positive real number as base to be raised to any real power, always producing a positive result, so logb(x) for any two positive real numbers b and x, where b is not equal to 1, is always a unique real number y. More explicitly, the defining relation between exponentiation and logarithm is:

logb(x)=y exactly if  by=x and  x>0 and  b>0 and  b≠1.
For example, log2 64 = 6, as 26 = 64. The logarithm base 10 (that is b = 10) is called the decimal or common logarithm and is commonly used in science and engineering. The natural logarithm has the number e (that is b ≈ 2.718) as its base; its use is widespread in mathematics and physics, because of its simpler integral and derivative. The binary logarithm uses base 2 (that is b = 2) and is frequently used in computer science. Logarithms are examples of concave functions.[317]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Logarithmic identities    Several important formulas, sometimes called logarithmic identities or log laws, relate logarithms to one another.[318]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Logarithmic mean temperature difference    (Also known as log mean temperature difference, LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. The LMTD is a logarithmic average of the temperature difference between the hot and cold feeds at each end of the double pipe exchanger. For a given heat exchanger with constant area and heat transfer coefficient, the larger the LMTD, the more heat is transferred. The use of the LMTD arises straightforwardly from the analysis of a heat exchanger with constant flow rate and fluid thermal properties.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Lumped capacitance model    A lumped-capacitance model, also called lumped system analysis,[319] reduces a thermal system to a number of discrete “lumps” and assumes that the temperature difference inside each lump is negligible. This approximation is useful to simplify otherwise complex differential heat equations. It was developed as a mathematical analog of electrical capacitance, although it also includes thermal analogs of electrical resistance as well.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Lumped element model    The lumped-element model (also called lumped-parameter model, or lumped-component model) simplifies the description of the behaviour of spatially distributed physical systems into a topology consisting of discrete entities that approximate the behaviour of the distributed system under certain assumptions. It is useful in electrical systems (including electronics), mechanical multibody systems, heat transfer, acoustics, etc. Mathematically speaking, the simplification reduces the state space of the system to a finite dimension, and the partial differential equations (PDEs) of the continuous (infinite-dimensional) time and space model of the physical system into ordinary differential equations (ODEs) with a finite number of parameters.

## M

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Macaulay's method    (The double integration method) is a technique used in structural analysis to determine the deflection of Euler-Bernoulli beams. Use of Macaulay’s technique is very convenient for cases of discontinuous and/or discrete loading. Typically partial uniformly distributed loads (u.d.l.) and uniformly varying loads (u.v.l.) over the span and a number of concentrated loads are conveniently handled using this technique.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mach number    The ratio of the speed of an object to the speed of sound.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Machine    A machine (or mechanical device) is a mechanical structure that uses power to apply forces and control movement to perform an intended action. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Machine code    In computer programming, machine code, consisting of machine language instructions, is a low-level programming language used to directly control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very specific task, such as a load, a store, a jump, or an arithmetic logic unit (ALU) operation on one or more units of data in the CPU's registers or memory.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Machine element    Or hardware, refers to an elementary component of a machine. These elements consist of three basic types:

1. structural components such as frame members, bearings, axles, splines, fasteners, seals, and lubricants,
2. mechanisms that control movement in various ways such as gear trains, belt or chain drives, linkages, cam and follower systems, including brakes and clutches, and
3. control components such as buttons, switches, indicators, sensors, actuators and computer controllers.[320]

While generally not considered to be a machine element, the shape, texture and color of covers are an important part of a machine that provide a styling and operational interface between the mechanical components of a machine and its users. Machine elements are basic mechanical parts and features used as the building blocks of most machines.[321] Most are standardized to common sizes, but customs are also common for specialized applications.[322]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Machine learning    (ML), is the study of computer algorithms that improve automatically through experience and by the use of data.[323] It is seen as a part of artificial intelligence. Machine learning algorithms build a model based on sample data, known as "training data", in order to make predictions or decisions without being explicitly programmed to do so.[324] Machine learning algorithms are used in a wide variety of applications, such as in medicine, email filtering, speech recognition, and computer vision, where it is difficult or unfeasible to develop conventional algorithms to perform the needed tasks.[325]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Maclaurin series    In mathematics, the Taylor series of a function is an infinite sum of terms that are expressed in terms of the function's derivatives at a single point. For most common functions, the function and the sum of its Taylor series are equal near this point. Taylor's series are named after Brook Taylor, who introduced them in 1715. If zero is the point where the derivatives are considered, a Taylor series is also called a Maclaurin series, after Colin Maclaurin, who made extensive use of this special case of Taylor series in the 18th century.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Magnetic field    A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents,[326]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". [327] and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field.[328]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". [329] A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors. In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter (A/m).[330] B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second2 per ampere),[331] which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum, the two fields are related through the vacuum permeability, 𝐁/μ0=𝐇; but in a magnetized material, the terms differ by the material's magnetization at each point.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Magnetism    Is a class of physical attributes that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomenon of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. The rare-earth metals neodymium and samarium are less common examples. The prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Manufacturing engineering    Is a branch of professional engineering that shares many common concepts and ideas with other fields of engineering such as mechanical, chemical, electrical, and industrial engineering. Manufacturing engineering requires the ability to plan the practices of manufacturing; to research and to develop tools, processes, machines and equipment; and to integrate the facilities and systems for producing quality products with the optimum expenditure of capital.[332] The manufacturing or production engineer's primary focus is to turn raw material into an updated or new product in the most effective, efficient & economic way possible.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mass balance    A mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have been unknown, or difficult to measure without this technique. The exact conservation law used in the analysis of the system depends on the context of the problem, but all revolve around mass conservation, i.e., that matter cannot disappear or be created spontaneously.[333]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24".
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mass density    The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:[334]

ρ=mV
where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume,[335] although this is scientifically inaccurate – this quantity is more specifically called specific weight.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mass moment of inertia    The moment of inertia, otherwise known as the mass moment of inertia, angular mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis, akin to how mass determines the force needed for a desired acceleration. It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rate of rotation.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mass number    The mass number (symbol A, from the German word Atomgewicht [atomic weight]),[336] also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approximately equal to the atomic (also known as isotopic) mass of the atom expressed in atomic mass units. Since protons and neutrons are both baryons, the mass number A is identical with the baryon number B of the nucleus (and also of the whole atom or ion). The mass number is different for each different isotope of a chemical element. Hence, the difference between the mass number and the atomic number Z gives the number of neutrons (N) in a given nucleus: N = A − Z.[337] The mass number is written either after the element name or as a superscript to the left of an element's symbol. For example, the most common isotope of carbon is carbon-12, or Lua error: Internal error: The interpreter has terminated with signal "24"., which has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: 126C.[338]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mass spectrometry    (MS), is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Material failure theory    Is an interdisciplinary field of materials science and solid mechanics which attempts to predict the conditions under which solid materials fail under the action of external loads. The failure of a material is usually classified into brittle failure (fracture) or ductile failure (yield). Depending on the conditions (such as temperature, state of stress, loading rate) most materials can fail in a brittle or ductile manner or both. However, for most practical situations, a material may be classified as either brittle or ductile. In mathematical terms, failure theory is expressed in the form of various failure criteria which are valid for specific materials. Failure criteria are functions in stress or strain space which separate "failed" states from "unfailed" states. A precise physical definition of a "failed" state is not easily quantified and several working definitions are in use in the engineering community. Quite often, phenomenological failure criteria of the same form are used to predict brittle failure and ductile yields.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Material properties    A materials property is an intensive property of some material, i.e., a physical property that does not depend on the amount of the material. These quantitative properties may be used as a metric by which the benefits of one material versus another can be compared, thereby aiding in materials selection.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Materials science    The interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of new materials, particularly solids. The intellectual origins of materials science stem from the Enlightenment, when researchers began to use analytical thinking from chemistry, physics, and engineering to understand ancient, phenomenological observations in metallurgy and mineralogy.[339][340] Materials science still incorporates elements of physics, chemistry, and engineering. As such, the field was long considered by academic institutions as a sub-field of these related fields. Beginning in the 1940s, materials science began to be more widely recognized as a specific and distinct field of science and engineering, and major technical universities around the world created dedicated schools for its study. Materials scientists emphasize understanding, how the history of a material (processing) influences its structure, and thus the material's properties and performance. The understanding of processing-structure-properties relationships is called the materials paradigm. This paradigm is used to advance understanding in a variety of research areas, including nanotechnology, biomaterials, and metallurgy. Materials science is also an important part of forensic engineering and failure analysis - investigating materials, products, structures or components, which fail or do not function as intended, causing personal injury or damage to property. Such investigations are key to understanding, for example, the causes of various aviation accidents and incidents.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mathematical optimization    Mathematical optimization (alternatively spelled optimisation) or mathematical programming is the selection of a best element, with regard to some criterion, from some set of available alternatives.[341] Optimization problems of sorts arise in all quantitative disciplines from computer science and engineering to operations research and economics, and the development of solution methods has been of interest in mathematics for centuries.[342] In the simplest case, an optimization problem consists of maximizing or minimizing a real function by systematically choosing input values from within an allowed set and computing the value of the function. The generalization of optimization theory and techniques to other formulations constitutes a large area of applied mathematics. More generally, optimization includes finding "best available" values of some objective function given a defined domain (or input), including a variety of different types of objective functions and different types of domains.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mathematical physics    Refers to the development of mathematical methods for application to problems in physics. The Journal of Mathematical Physics defines the field as "the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and for the formulation of physical theories".[343]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mathematics    Includes the study of such topics as quantity (number theory),[344] structure (algebra),[345] space (geometry),[344] and change (analysis).[346][347][348] It has no generally accepted definition.[349][350] Mathematicians seek and use patterns[351][352] to formulate new conjectures; they resolve the truth or falsity of such by mathematical proof. When mathematical structures are good models of real phenomena, mathematical reasoning can be used to provide insight or predictions about nature. Through the use of abstraction and logic, mathematics developed from counting, calculation, measurement, and the systematic study of the shapes and motions of physical objects. Practical mathematics has been a human activity from as far back as written records exist. The research required to solve mathematical problems can take years or even centuries of sustained inquiry.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Matrix    In mathematics, a matrix (plural matrices) is a rectangular array or table of numbers, symbols, or expressions, arranged in rows and columns, which is used to represent a mathematical object or a property of such an object. For example,

[19−13205−6]
is a matrix with two rows and three columns; one say often a "two by three matrix", a "2×3-matrix", or a matrix of dimension 2×3. Without further specifications, matrices represent linear maps, and allow explicit computations in linear algebra. Therefore, the study of matrices is a large part of linear algebra, and most properties and operations of abstract linear algebra can be expressed in terms of matrices. For example, matrix multiplication represents composition of linear maps. Not all matrices are related to linear algebra. This is in particular the case, in graph theory, of incidence matrices and adjacency matrices.[353]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Matter    In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume.[354] All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, "matter" generally includes atoms and anything made up of them, and any particles (or combination of particles) that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light.[354]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". [355] Matter exists in various states (also known as phases). These include classical everyday phases such as solid, liquid, and gas – for example water exists as ice, liquid water, and gaseous steam – but other states are possible, including plasma, Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.[356]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Maximum-distortion energy theory    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Maximum-normal-stress theory    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Maximum shear stress    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Maxwell's equations    Are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits. The equations provide a mathematical model for electric, optical, and radio technologies, such as power generation, electric motors, wireless communication, lenses, radar etc. They describe how electric and magnetic fields are generated by charges, currents, and changes of the fields.[note 3] The equations are named after the physicist and mathematician James Clerk Maxwell, who, in 1861 and 1862, published an early form of the equations that included the Lorentz force law. Maxwell first used the equations to propose that light is an electromagnetic phenomenon. An important consequence of Maxwell's equations is that they demonstrate how fluctuating electric and magnetic fields propagate at a constant speed (c) in a vacuum. Known as electromagnetic radiation, these waves may occur at various wavelengths to produce a spectrum of light from radio waves to gamma rays.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mean    There are several kinds of mean in mathematics, especially in statistics: For a data set, the arithmetic mean, also known as average or arithmetic average, is a central value of a finite set of numbers: specifically, the sum of the values divided by the number of values. The arithmetic mean of a set of numbers x1, x2, ..., xn is typically denoted by x¯[note 4]. If the data set were based on a series of observations obtained by sampling from a statistical population, the arithmetic mean is the sample mean (denoted x¯) to distinguish it from the mean, or expected value, of the underlying distribution, the population mean (denoted μ or μx[note 5]).[328][357] In probability and statistics, the population mean, or expected value, is a measure of the central tendency either of a probability distribution or of a random variable characterized by that distribution.[358] In a discrete probability distribution of a random variable X, the mean is equal to the sum over every possible value weighted by the probability of that value; that is, it is computed by taking the product of each possible value x of X and its probability p(x), and then adding all these products together, giving μ=∑xp(x).....[359][360] An analogous formula applies to the case of a continuous probability distribution. Not every probability distribution has a defined mean (see the Cauchy distribution for an example). Moreover, the mean can be infinite for some distributions. For a finite population, the population mean of a property is equal to the arithmetic mean of the given property, while considering every member of the population. For example, the population mean height is equal to the sum of the heights of every individual—divided by the total number of individuals. The sample mean may differ from the population mean, especially for small samples. The law of large numbers states that the larger the size of the sample, the more likely it is that the sample mean will be close to the population mean.[361] Outside probability and statistics, a wide range of other notions of mean are often used in geometry and mathematical analysis.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Measure of central tendency    In statistics, a central tendency (or measure of central tendency) is a central or typical value for a probability distribution.[362] It may also be called a center or location of the distribution. Colloquially, measures of central tendency are often called averages. The term central tendency dates from the late 1920s.[363] The most common measures of central tendency are the arithmetic mean, the median, and the mode. A middle tendency can be calculated for either a finite set of values or for a theoretical distribution, such as the normal distribution. Occasionally authors use central tendency to denote "the tendency of quantitative data to cluster around some central value."[363][364] The central tendency of a distribution is typically contrasted with its dispersion or variability; dispersion and central tendency are the often characterized properties of distributions. Analysis may judge whether data has a strong or a weak central tendency based on its dispersion.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanical advantage    Is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for this is the law of the lever. Machine components designed to manage forces and movement in this way are called mechanisms.[365] An ideal mechanism transmits power without adding to or subtracting from it. This means the ideal mechanism does not include a power source, is frictionless, and is constructed from rigid bodies that do not deflect or wear. The performance of a real system relative to this ideal is expressed in terms of efficiency factors that take into account departures from the ideal.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanical engineering    Is an engineering branch that combines engineering physics and mathematics principles with materials science to design, analyze, manufacture, and maintain mechanical systems.[366] It is one of the oldest and broadest of the engineering branches.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanical filter    Is a signal processing filter usually used in place of an electronic filter at radio frequencies. Its purpose is the same as that of a normal electronic filter: to pass a range of signal frequencies, but to block others. The filter acts on mechanical vibrations which are the analogue of the electrical signal. At the input and output of the filter, transducers convert the electrical signal into, and then back from, these mechanical vibrations.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanical wave    Is a wave that is an oscillation of matter, and therefore transfers energy through a medium.[367] While waves can move over long distances, the movement of the medium of transmission—the material—is limited. Therefore, the oscillating material does not move far from its initial equilibrium position. Mechanical waves transport energy. This energy propagates in the same direction as the wave. Any kind of wave (mechanical or electromagnetic) has a certain energy. Mechanical waves can be produced only in media which possess elasticity and inertia.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanics    Is the area of physics concerned with the motions of physical objects, more specifically the relationships among force, matter, and motion.[368] Forces applied to objects result in displacements, or changes of an object's position relative to its environment. This branch of physics has its origins in Ancient Greece with the writings of Aristotle and Archimedes[369][370][371] (see History of classical mechanics and Timeline of classical mechanics). During the early modern period, scientists such as Galileo, Kepler, and Newton laid the foundation for what is now known as classical mechanics. It is a branch of classical physics that deals with particles that are either at rest or are moving with velocities significantly less than the speed of light. It can also be defined as a branch of science which deals with the motion of and forces on bodies not in the quantum realm. The field is today less widely understood in terms of quantum theory.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mechanism    Is a device that transforms input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components which may include:

* Gears and gear trains;
* Belts and chain drives;
* Cams and followers;
* Linkages;
* Friction devices, such as brakes or clutches;
* Structural components such as a frame, fasteners, bearings, springs, or lubricants;
* Various machine elements, such as splines, pins, or keys.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Median    In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic feature of the median in describing data compared to the mean (often simply described as the "average") is that it is not skewed by a small proportion of extremely large or small values, and therefore provides a better representation of a "typical" value. Median income, for example, may be a better way to suggest what a "typical" income is, because income distribution can be very skewed. The median is of central importance in robust statistics, as it is the most resistant statistic, having a breakdown point of 50%: so long as no more than half the data are contaminated, the median is not an arbitrarily large or small result.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Melting    Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Melting point    The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of substances to supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the melting point."[372]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Meson    In particle physics, mesons are hadronic subatomic particles composed of an equal number of quarks and antiquarks, usually one of each, bound together by strong interactions. Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one femtometer (1×10−15 m),[373] which is about 0.6 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Heavier mesons decay to lighter mesons and ultimately to stable electrons, neutrinos and photons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Metallic bonding    Is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be described as the sharing of free electrons among a structure of positively charged ions (cations). Metallic bonding accounts for many physical properties of metals, such as strength, ductility, thermal and electrical resistivity and conductivity, opacity, and luster.[374][375][376][377] Metallic bonding is not the only type of chemical bonding a metal can exhibit, even as a pure substance. For example, elemental gallium consists of covalently-bound pairs of atoms in both liquid and solid-state—these pairs form a crystal structure with metallic bonding between them. Another example of a metal–metal covalent bond is the mercurous ion (Hg2+2).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Middle-out     A combination of top-down and bottom-up design.[378]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mid-range    In statistics, the mid-range or mid-extreme is a measure of central tendency of a sample (statistics) defined as the arithmetic mean of the maximum and minimum values of the data set:Lua error: Internal error: The interpreter has terminated with signal "24".Lua error: Internal error: The interpreter has terminated with signal "24".

M=max⁡x+min⁡x2.
The mid-range is closely related to the range, a measure of statistical dispersion defined as the difference between maximum and minimum values. The two measures are complementary in sense that if one knows the mid-range and the range, one can find the sample maximum and minimum values. The mid-range is rarely used in practical statistical analysis, as it lacks efficiency as an estimator for most distributions of interest, because it ignores all intermediate points, and lacks robustness, as outliers change it significantly. Indeed, it is one of the least efficient and least robust statistics. However, it finds some use in special cases: it is the maximally efficient estimator for the center of a uniform distribution, trimmed mid-ranges address robustness, and as an L-estimator, it is simple to understand and compute.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Midhinge    In statistics, the midhinge is the average of the first and third quartiles and is thus a measure of location. Equivalently, it is the 25% trimmed mid-range or 25% midsummary; it is an L-estimator.

MH⁡(X)=Q1,3(X)‾=Q1(X)+Q3(X)2=P25(X)+P75(X)2=M25(X)
The midhinge is related to the interquartile range (IQR), the difference of the third and first quartiles (i.e. IQR=Q3−Q1), which is a measure of statistical dispersion. The two are complementary in sense that if one knows the midhinge and the IQR, one can find the first and third quartiles. The use of the term "hinge" for the lower or upper quartiles derives from John Tukey's work on exploratory data analysis in the late 1970s,[379] and "midhinge" is a fairly modern term dating from around that time. The midhinge is slightly simpler to calculate than the trimean (TM), which originated in the same context and equals the average of the median (X~=Q2=P50) and the midhinge.

MH⁡(X)=2TM⁡(X)−med⁡(X)=2Q1+2Q2+Q34−Q2

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mining engineering

Mining in the engineering discipline is the extraction of minerals from underneath, above or on the ground. Mining engineering is associated with many other disciplines, such as mineral processing, exploration, excavation, geology, and metallurgy, geotechnical engineering and surveying. A mining engineer may manage any phase of mining operations, from exploration and discovery of the mineral resources, through feasibility study, mine design, development of plans, production and operations to mine closure.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Miller indices

Miller indices form a notation system in crystallography for planes in crystal (Bravais) lattices. In particular, a family of lattice planes is determined by three integers h, k, and ℓ, the Miller indices. They are written (hkℓ), and denote the family of planes orthogonal to hb𝟏+kb𝟐+ℓb𝟑, where b𝐢 are the basis of the reciprocal lattice vectors (note that the plane is not always orthogonal to the linear combination of direct lattice vectors ha𝟏+ka𝟐+ℓa𝟑 because the lattice vectors need not be mutually orthogonal). By convention, negative integers are written with a bar, as in 3 for −3. The integers are usually written in lowest terms, i.e. their greatest common divisor should be 1\. Miller indices are also used to designate reflections in X-ray crystallography. In this case the integers are not necessarily in lowest terms, and can be thought of as corresponding to planes spaced such that the reflections from adjacent planes would have a phase difference of exactly one wavelength (2π), regardless of whether there are atoms on all these planes or not. There are also several related notations:[380]

* the notation {hkℓ} denotes the set of all planes that are equivalent to (hkℓ) by the symmetry of the lattice.

In the context of crystal directions (not planes), the corresponding notations are:

* [hkℓ], with square instead of round brackets, denotes a direction in the basis of the direct lattice vectors instead of the reciprocal lattice; and
* similarly, the notation <hkℓ> denotes the set of all directions that are equivalent to [hkℓ] by symmetry.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mobile robot

Is a robot that is capable of moving in the surrounding (locomotion).[381] Mobile robotics is usually considered to be a subfield of robotics and information engineering.[382] Mobile robots have the capability to move around in their environment and are not fixed to one physical location. Mobile robots can be "autonomous" (AMR - autonomous mobile robot) which means they are capable of navigating an uncontrolled environment without the need for physical or electro-mechanical guidance devices.[383] Alternatively, mobile robots can rely on guidance devices that allow them to travel a pre-defined navigation route in relatively controlled space.[384] By contrast, industrial robots are usually more-or-less stationary, consisting of a jointed arm (multi-linked manipulator) and gripper assembly (or end effector), attached to a fixed surface. The joint-arm are controlled by linear actuator or servo motor or stepper motor.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mode

The mode is the value that appears most often in a set of data values.[385] If X is a discrete random variable, the mode is the value x (i.e, X = x) at which the probability mass function takes its maximum value. In other words, it is the value that is most likely to be sampled. Like the statistical mean and median, the mode is a way of expressing, in a (usually) single number, important information about a random variable or a population. The numerical value of the mode is the same as that of the mean and median in a normal distribution, and it may be very different in highly skewed distributions.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Modulus of elasticity

An elastic modulus (also known as modulus of elasticity) is a quantity that measures an object or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region:[386] A stiffer material will have a higher elastic modulus. An elastic modulus has the form:

δ =def stressstrain
where stress is the force causing the deformation divided by the area to which the force is applied and strain is the ratio of the change in some parameter caused by the deformation to the original value of the parameter. Since strain is a dimensionless quantity, the units of δ will be the same as the units of stress.[387]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mohr's circle

A graphical method of analyzing the three-dimensional stresses in a system that has a loading force applied to it.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molality

Is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution. A commonly used unit for molality in chemistry is mol/kg. A solution of concentration 1 mol/kg is also sometimes denoted as 1 molal. The unit mol/kg requires that molar mass be expressed in kg/mol, instead of the usual g/mol or kg/kmol.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molar attenuation coefficient

Is a measurement of how strongly a chemical species attenuates light at a given wavelength. It is an intrinsic property of the species. The SI unit of molar attenuation coefficient is the square metre per mole (m2/mol), but in practice, quantities are usually expressed in terms of M−1⋅cm−1 or L⋅mol−1⋅cm−1 (the latter two units are both equal to 0.1 m2/mol). In older literature, the cm2/mol is sometimes used; 1 M−1⋅cm−1 equals 1000 cm2/mol. The molar attenuation coefficient is also known as the molar extinction coefficient and molar absorptivity, but the use of these alternative terms has been discouraged by the IUPAC.[388][389]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molar concentration

Molar concentration (also called molarity, amount concentration or substance concentration) is a measure of the concentration of a chemical species, in particular of a solute in a solution, in terms of amount of substance per unit volume of solution. In chemistry, the most commonly used unit for molarity is the number of moles per liter, having the unit symbol mol/L or mol⋅dm−3 in SI unit. A solution with a concentration of 1 mol/L is said to be 1 molar, commonly designated as 1 M. To avoid confusion with SI prefix mega, which has the same abbreviation, small caps ᴍ or italicized M are also used in journals and textbooks.[390]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molar mass

In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance in that sample, measured in moles.[391] It is the mass of 1 mole of the substance or Lua error: Internal error: The interpreter has terminated with signal "24". particles, expressed in grams. The molar mass is a bulk, not molecular, property of a substance. The molar mass is an average of many instances of the compound, which often vary in mass due to the presence of isotopes. Most commonly, the molar mass is computed from the standard atomic weights and is thus a terrestrial average and a function of the relative abundance of the isotopes of the constituent atoms on Earth. The molar mass is appropriate for converting between the mass of a substance and the amount of a substance for bulk quantities.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molding

Molding (American English) or moulding (British and Commonwealth English; see spelling differences) is the process of manufacturing by shaping liquid or pliable raw material using a rigid frame called a mold or matrix.[392] This itself may have been made using a pattern or model of the final object.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molecule

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.[393][394][395][396][397] Molecules are distinguished from ions by their lack of electrical charge. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions. In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. This violates the definition that a molecule contain two or more atoms, since the noble gases are individual atoms.[398] A molecule may be homonuclear, that is, it consists of atoms of one chemical element, as with two atoms in the oxygen molecule (O2); or it may be heteronuclear, a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H2O). Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are typically not considered single molecules.[399]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Molecular physics

Is the study of the physical properties of molecules, the chemical bonds between atoms as well as the molecular dynamics. Its most important experimental techniques are the various types of spectroscopy; scattering is also used. The field is closely related to atomic physics and overlaps greatly with theoretical chemistry, physical chemistry and chemical physics.[400]

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Moment of inertia

The moment of inertia, otherwise known as the mass moment of inertia, angular mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular acceleration about a rotational axis, akin to how mass determines the force needed for a desired acceleration. It depends on the body's mass distribution and the axis chosen, with larger moments requiring more torque to change the body's rate of rotation.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Multibody system

Is the study of the dynamic behavior of interconnected rigid or flexible bodies, each of which may undergo large translational and rotational displacements.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Multidisciplinary design optimization

(MDO), is a field of engineering that uses optimization methods to solve design problems incorporating a number of disciplines. It is also known as multidisciplinary system design optimization (MSDO). MDO allows designers to incorporate all relevant disciplines simultaneously. The optimum of the simultaneous problem is superior to the design found by optimizing each discipline sequentially, since it can exploit the interactions between the disciplines. However, including all disciplines simultaneously significantly increases the complexity of the problem.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Mutual inductance

Is the ratio between the electromotive force induced in one loop or coil by the rate of change of current in another loop or coil. Mutual inductance is given the symbol M.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Muon

The muon, from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not known to have any sub-structure – that is, it is not thought to be composed of any simpler particles. The muon is an unstable subatomic particle with a mean lifetime of Lua error: Internal error: The interpreter has terminated with signal "24"., much longer than many other subatomic particles. As with the decay of the non-elementary neutron (with a lifetime around 15 minutes), muon decay is slow (by subatomic standards) because the decay is mediated only by the weak interaction (rather than the more powerful strong interaction or electromagnetic interaction), and because the mass difference between the muon and the set of its decay products is small, providing few kinetic degrees of freedom for decay. Muon decay almost always produces at least three particles, which must include an electron of the same charge as the muon and two types of neutrinos.

## N

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nanoengineering    Is the practice of engineering on the nanoscale. It derives its name from the nanometre, a unit of measurement equalling one billionth of a meter. Nanoengineering is largely a synonym for nanotechnology, but emphasizes the engineering rather than the pure science aspects of the field.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nanotechnology    The technology of systems built with moving parts on the order of a nanometre in size.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Navier–Stokes equations    In physics, the Navier–Stokes equations are a set of partial differential equations which describe the motion of viscous fluid substances, named after French engineer and physicist Claude-Louis Navier and Anglo-Irish physicist and mathematician George Gabriel Stokes.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Neutrino    A neutrino (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of Lua error: Internal error: The interpreter has terminated with signal "24".) that interacts only via the weak subatomic force and gravity.[401][402] The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The mass of the neutrino is much smaller than that of the other known elementary particles.[403] The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction.[404] Thus, neutrinos typically pass through normal matter unimpeded and undetected.[405][402]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Newtonian fluid    Is a fluid in which the viscous stresses arising from its flow, at every point, are linearly[406] correlated to the local strain rate—the rate of change of its deformation over time.[407][408][409] That is equivalent to saying those forces are proportional to the rates of change of the fluid's velocity vector as one moves away from the point in question in various directions. More precisely, a fluid is Newtonian only if the tensors that describe the viscous stress and the strain rate are related by a constant viscosity tensor that does not depend on the stress state and velocity of the flow. If the fluid is also isotropic (that is, its mechanical properties are the same along any direction), the viscosity tensor reduces to two real coefficients, describing the fluid's resistance to continuous shear deformation and continuous compression or expansion, respectively.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Norton's theorem    In direct-current circuit theory, Norton's theorem (aka Mayer–Norton theorem) is a simplification that can be applied to networks made of linear time-invariant resistances, voltage sources, and current sources. At a pair of terminals of the network, it can be replaced by a current source and a single resistor in parallel. For alternating current (AC) systems the theorem can be applied to reactive impedances as well as resistances.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nozzle    Is a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to direct or modify the flow of a fluid (liquid or gas). Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them. In a nozzle, the velocity of fluid increases at the expense of its pressure energy.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">nth root    To put a number of function to the exponential power of 1/n.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear binding energy    The difference between the total mass energy of a nucleus and the mass energy of the isolated nucleons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear engineering    The profession that deals with nuclear power.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear fusion    Is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products is manifested as either the release or the absorption of energy. This difference in mass arises due to the difference in atomic binding energy between the nuclei before and after the reaction. Fusion is the process that powers active or main sequence stars and other high-magnitude stars, where large amounts of energy are released.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear physics    The science that describes the components of atoms.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear potential energy    The energy that is given up in decay of an unstable nucleus.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Nuclear power    The use of energy derived from nuclear chain reactions for electricity production or ship propulsion.

## O

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ohm    The SI unit of electrical resistance.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ohm's law    A law describing the relationship between resistance, current, and voltage.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Optics    The study of light.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Organic chemistry    The study of carbon compounds.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Osmosis    The spontaneous movement of molecules or ions through a semi-permable membrane, tending to equalize concentration on both sides.

## P

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Parallel circuit    A circuit that begins and ends at the same node as another circuit.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Parity (mathematics)    In mathematics, parity is the property of an integer of whether it is even or odd. An integer's parity is even if it is divisible by two with no remainders left and its parity is odd if its remainder is 1.[410] For example, -4, 0, 82, and 178 are even because there is no remainder when dividing it by 2. By contrast, -3, 5, 7, 21 are odd numbers as they leave a remainder of 1 when divided by 2.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Parity    In quantum mechanics, a parity transformation (also called parity inversion) is the flip in the sign of one spatial coordinate. In three dimensions, it can also refer to the simultaneous flip in the sign of all three spatial coordinates (a point reflection):

𝐏:(xyz)↦(−x−y−z).
It can also be thought of as a test for chirality of a physical phenomenon, in that a parity inversion transforms a phenomenon into its mirror image. All fundamental interactions of elementary particles, with the exception of the weak interaction, are symmetric under parity. The weak interaction is chiral and thus provides a means for probing chirality in physics. In interactions that are symmetric under parity, such as electromagnetism in atomic and molecular physics, parity serves as a powerful controlling principle underlying quantum transitions. A matrix representation of P (in any number of dimensions) has determinant equal to −1, and hence is distinct from a rotation, which has a determinant equal to 1. In a two-dimensional plane, a simultaneous flip of all coordinates in sign is not a parity transformation; it is the same as a 180°-rotation. In quantum mechanics, wave functions that are unchanged by a parity transformation are described as even functions, while those that change sign under a parity transformation are odd functions.fn=A hydrocarbon compound, solid at room temperature.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Paramagnetism    Is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field.[411] Paramagnetic materials include most chemical elements and some compounds;[412] they have a relative magnetic permeability slightly greater than 1 (i.e., a small positive magnetic susceptibility) and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Particle accelerator    Is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.[413]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Particle displacement    Particle displacement or displacement amplitude is a measurement of distance of the movement of a sound particle from its equilibrium position in a medium as it transmits a sound wave.[414] The SI unit of particle displacement is the metre (m). In most cases this is a longitudinal wave of pressure (such as sound), but it can also be a transverse wave, such as the vibration of a taut string. In the case of a sound wave travelling through air, the particle displacement is evident in the oscillations of air molecules with, and against, the direction in which the sound wave is travelling.[415]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Particle physics    Particle physics (also known as high energy physics) is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word particle can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), particle physics usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour. In current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity.[416][417]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pascal's law    Pascal's law (also Pascal's principle[418][419][420] or the principle of transmission of fluid-pressure) is a principle in fluid mechanics that states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere.[421] The law was established by French mathematician Blaise Pascal[30] in 1647–48.[422]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pendulum    Is a weight suspended from a pivot so that it can swing freely.[423] When a pendulum is displaced sideways from its resting, equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. When released, the restoring force acting on the pendulum's mass causes it to oscillate about the equilibrium position, swinging back and forth. The time for one complete cycle, a left swing and a right swing, is called the period. The period depends on the length of the pendulum and also to a slight degree on the amplitude, the width of the pendulum's swing.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Petroleum engineering    Is a field of engineering concerned with the activities related to the production of Hydrocarbons, which can be either crude oil or natural gas.[424] Exploration and production are deemed to fall within the upstream sector of the oil and gas industry. Exploration, by earth scientists, and petroleum engineering are the oil and gas industry's two main subsurface disciplines, which focus on maximizing economic recovery of hydrocarbons from subsurface reservoirs. Petroleum geology and geophysics focus on provision of a static description of the hydrocarbon reservoir rock, while petroleum engineering focuses on estimation of the recoverable volume of this resource using a detailed understanding of the physical behavior of oil, water and gas within porous rock at very high pressure.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">pH    A logarithmic measure of the concentration of hydrogen ions in an acid or base solution.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Phase (matter)    In the physical sciences, a phase is a region of space (a thermodynamic system), throughout which all physical properties of a material are essentially uniform.[425][426]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". [427]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". Examples of physical properties include density, index of refraction, magnetization and chemical composition. A simple description is that a phase is a region of material that is chemically uniform, physically distinct, and (often) mechanically separable. In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air is a third phase over the ice and water. The glass of the jar is another separate phase. (See Lua error: Internal error: The interpreter has terminated with signal "24".)
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Phase (waves)    In physics and mathematics, the phase of a periodic function F of some real variable t (such as time) is an angle-like quantity representing the fraction of the cycle covered up to t. It is denoted ϕ(t) and expressed in such a scale that it varies by one full turn as the variable t goes through each period (and F(t) goes through each complete cycle). It may be measured in any angular unit such as degrees or radians, thus increasing by 360° or 2π as the variable t completes a full period.[428]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Phase diagram    A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases (such as solid, liquid or gaseous states) occur and coexist at equilibrium.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Phase rule    In thermodynamics, the phase rule is a general principle governing "pVT" systems (that is, systems whose states are completely described by the variables pressure (p), volume (V) and temperature (T)) in thermodynamic equilibrium. If F is the number of degrees of freedom, C is the number of components and P is the number of phases, then[429][102]

F=C−P+2.
It was derived by American physicist Josiah Willard Gibbs in his landmark paper titled On the Equilibrium of Heterogeneous Substances, published in parts between 1875 and 1878.[430] The rule assumes the components do not react with each other.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Photon    Is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless,[lower-alpha 3] so they always move at the speed of light in vacuum, Lua error: Internal error: The interpreter has terminated with signal "24". (or about Lua error: Internal error: The interpreter has terminated with signal "24".). The photon belongs to the class of bosons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Physical chemistry    Is the study of macroscopic, and particulate phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibrium.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Physical quantity    A physical quantity is a property of a material or system that can be quantified by measurement. A physical quantity can be expressed as a value, which is the algebraic multiplication of a numerical value and a unit. For example, the physical quantity mass can be quantified as n kg, where n is the numerical value and kg is the unit. A physical quantity possesses at least two characteristics in common. One is numerical magnitude and the other is the unit in which it is measured.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Physics    Is the natural science that studies matter,[lower-alpha 4] its motion and behavior through space and time, and the related entities of energy and force.[432] Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.[lower-alpha 5][433][434][435]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Planck constant    The Planck constant, or Planck's constant, is a fundamental physical constant denoted h, and is of fundamental importance in quantum mechanics. A photon's energy is equal to its frequency multiplied by the Planck constant. Due to mass–energy equivalence, the Planck constant also relates mass to frequency. In metrology it is used, together with other constants, to define the kilogram, an SI unit.[436] The SI units are defined in such a way that, when the Planck constant is expressed in SI units, it has the exact value h = Lua error: Internal error: The interpreter has terminated with signal "24"..[437][438]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Plasma    Is one of the four fundamental states of matter, first systematically studied by Irving Langmuir in the 1920s.[439][440] It consists of a gas of ions – atoms or molecules which have one or more orbital electrons stripped (or, rarely, an extra electron attached), and free electrons.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Plasticity    In physics and materials science, plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces.[441][442] For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the material itself. In engineering, the transition from elastic behavior to plastic behavior is known as yielding.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pneumatics    The control of mechanical force and movement, generated by the application of compressed gas.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Point estimation    In statistics, point estimation involves the use of sample data to calculate a single value (known as a point estimate since it identifies a point in some parameter space) which is to serve as a "best guess" or "best estimate" of an unknown population parameter (for example, the population mean). More formally, it is the application of a point estimator to the data to obtain a point estimate. Point estimation can be contrasted with interval estimation: such interval estimates are typically either confidence intervals, in the case of frequentist inference, or credible intervals, in the case of Bayesian inference. More generally, a point estimator can be contrasted with a set estimator. Examples are given by confidence sets or credible sets. A point estimator can also be contrasted with a distribution estimator. Examples are given by confidence distributions, randomized estimators, and Bayesian posteriors.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Polyphase system    An electrical system that uses a set of alternating currents at different phases.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Power (electric)    Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes (as domestic mains electricity) by the electric power industry through an electric power grid. Electric power can be delivered over long distances by transmission lines and used for applications such as motion, light or heat with high efficiency.[443]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Power    In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, power is sometimes called activity.[444][445][446] Power is a scalar quantity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Power factor    In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit, and is a dimensionless number in the closed interval of −1 to 1. A power factor of less than one indicates the voltage and current are not in phase, reducing the average product of the two. Real power is the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of RMS current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power. A negative power factor occurs when the device (which is normally the load) generates power, which then flows back towards the source.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pressure    Pressure (symbol: p or P) is the force applied perpendicular to the surface of an object per unit area over which that force is distributed.<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". [447] Gauge pressure (also spelled gage pressure)[lower-alpha 6] is the pressure relative to the ambient pressure. Various units are used to express pressure. Some of these derive from a unit of force divided by a unit of area; the SI unit of pressure, the pascal (Pa), for example, is one newton per square metre (N/m2); similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and U.S. customary systems. Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure, and the torr is defined as ​1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, and inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Probability    Is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speaking, 0 indicates impossibility of the event and 1 indicates certainty.[note 6][448][449] The higher the probability of an event, the more likely it is that the event will occur. A simple example is the tossing of a fair (unbiased) coin. Since the coin is fair, the two outcomes ("heads" and "tails") are both equally probable; the probability of "heads" equals the probability of "tails"; and since no other outcomes are possible, the probability of either "heads" or "tails" is 1/2 (which could also be written as 0.5 or 50%).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Probability distribution    In probability theory and statistics, a probability distribution is the mathematical function that gives the probabilities of occurrence of different possible outcomes for an experiment.[450][451] It is a mathematical description of a random phenomenon in terms of its sample space and the probabilities of events (subsets of the sample space).[360] For instance, if X is used to denote the outcome of a coin toss ("the experiment"), then the probability distribution of X would take the value 0.5 (1 in 2 or 1/2) for X = heads, and 0.5 for X = tails (assuming that the coin is fair). Examples of random phenomena include the weather condition in a future date, the height of a randomly selected person, the fraction of male students in a school, the results of a survey to be conducted, etc.[452]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Probability theory    is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expressing it through a set of axioms. Typically these axioms formalise probability in terms of a probability space, which assigns a measure taking values between 0 and 1, termed the probability measure, to a set of outcomes called the sample space. Any specified subset of these outcomes is called an event. Central subjects in probability theory include discrete and continuous random variables, probability distributions, and stochastic processes, which provide mathematical abstractions of non-deterministic or uncertain processes or measured quantities that may either be single occurrences or evolve over time in a random fashion. Although it is not possible to perfectly predict random events, much can be said about their behavior. Two major results in probability theory describing such behaviour are the law of large numbers and the central limit theorem. As a mathematical foundation for statistics, probability theory is essential to many human activities that involve quantitative analysis of data.[453] Methods of probability theory also apply to descriptions of complex systems given only partial knowledge of their state, as in statistical mechanics or sequential estimation. A great discovery of twentieth-century physics was the probabilistic nature of physical phenomena at atomic scales, described in quantum mechanics.[454]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pulley    Is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, and the pulley may be called a sheave. A pulley may have a groove or grooves between flanges around its circumference to locate the cable or belt. The drive element of a pulley system can be a rope, cable, belt, or chain.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Pump    Is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift, displacement, and gravity pumps.[455] Pumps operate by some mechanism (typically reciprocating or rotary), and consume energy to perform mechanical work moving the fluid. Pumps operate via many energy sources, including manual operation, electricity, engines, or wind power, and come in many sizes, from microscopic for use in medical applications, to large industrial pumps.

## Q

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Quantum electrodynamics    In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Quantum field theory    In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity and quantum mechanics,[456]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". but not general relativity's description of gravity. QFT is used in particle physics to construct physical models of subatomic particles and in condensed matter physics to construct models of quasiparticles.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Quantum mechanics    Is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.[457]<span title="Lua error: Internal error: The interpreter has terminated with signal "24".">: Lua error: Internal error: The interpreter has terminated with signal "24". It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.

## R

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Regelation    The phenomena of melting under pressure, then freezing when the pressure is reduced.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Relative density    Relative density, or specific gravity,[458][459] is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest (at Lua error: Internal error: The interpreter has terminated with signal "24".); for gases, the reference is air at room temperature (Lua error: Internal error: The interpreter has terminated with signal "24".). The term "relative density" is often preferred in scientific usage.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Relative velocity    The relative velocity v→B∣A (also v→BA or v→Brel⁡A) is the velocity of an object or observer B in the rest frame of another object or observer A.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Reliability engineering    Is a sub-discipline of systems engineering that emphasizes the ability of equipment to function without failure. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time.[460] Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Resistivity    Electrical resistivity (also called specific electrical resistance or volume resistivity) and its inverse, electrical conductivity, is a fundamental property of a material that quantifies how strongly it resists or conducts electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm-meter (Ω⋅m).[461][462][463] For example, if a 1 m × 1 m × 1 m solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Resistor    Is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Reynolds number    The Reynolds number (Re) helps predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent. The turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). These eddy currents begin to churn the flow, using up energy in the process, which for liquids increases the chances of cavitation. Reynolds numbers are an important dimensionless quantity in fluid mechanics.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Rheology    Is the study of the flow of matter, primarily in a liquid or gas state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force. Rheology is a branch of physics, and it is the science that deals with the deformation and flow of materials, both solids and liquids.[464]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Rigid body    In physics, a rigid body (also known as a rigid object [465]) is a solid body in which deformation is zero or so small it can be neglected. The distance between any two given points on a rigid body remains constant in time regardless of external forces or moments exerted on it. A rigid body is usually considered as a continuous distribution of mass. In the study of special relativity, a perfectly rigid body does not exist; and objects can only be assumed to be rigid if they are not moving near the speed of light. In quantum mechanics, a rigid body is usually thought of as a collection of point masses. For instance, molecules (consisting of the point masses: electrons and nuclei) are often seen as rigid bodies (see classification of molecules as rigid rotors).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Robonaut    A development project conducted by NASA to create humanoid robots capable of using space tools and working in similar environments to suited astronauts.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Robot-assisted surgery    Robotic surgery are types of surgical procedures that are done using robotic systems. Robotically-assisted surgery was developed to try to overcome the limitations of pre-existing minimally-invasive surgical procedures and to enhance the capabilities of surgeons performing open surgery. In the case of robotically-assisted minimally-invasive surgery, instead of directly moving the instruments, the surgeon uses one of two methods to administer the instruments. These include using a direct telemanipulator or through computer control. A telemanipulator is a remote manipulator that allows the surgeon to perform the normal movements associated with the surgery. The robotic arms carry out those movements using end-effectors and manipulators to perform the actual surgery. In computer-controlled systems, the surgeon uses a computer to control the robotic arms and its end-effectors, though these systems can also still use telemanipulators for their input. One advantage of using the computerized method is that the surgeon does not have to be present, leading to the possibility for remote surgery.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Robotics    Is an interdisciplinary field that integrates computer science and engineering.[466] Robotics involves design, construction, operation, and use of robots. The goal of robotics is to design machines that can help and assist humans. Robotics integrates fields of mechanical engineering, electrical engineering, information engineering, mechatronics, electronics, bioengineering, computer engineering, control engineering, software engineering, among others.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Root mean square    In mathematics and its applications, the root mean square (RMS or rms) is defined as the square root of the mean square (the arithmetic mean of the squares of a set of numbers).[467] The RMS is also known as the quadratic mean[468][469] and is a particular case of the generalized mean with exponent 2\. RMS can also be defined for a continuously varying function in terms of an integral of the squares of the instantaneous values during a cycle. For alternating electric current, RMS is equal to the value of the constant direct current that would produce the same power dissipation in a resistive load.[467] In estimation theory, the root-mean-square deviation of an estimator is a measure of the imperfection of the fit of the estimator to the data.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Root-mean-square speed    In the physics of gas molecules, the root-mean-square speed is defined as the square root of the average squared-speed. The RMS speed of an ideal gas is calculated using the following equation:

vRMS=3RTM
where R represents the gas constant, 8.314 J/(mol·K), T is the temperature of the gas in kelvins, and M is the molar mass of the gas in kilograms per mole. In physics, speed is defined as the scalar magnitude of velocity. For a stationary gas, the average speed of its molecules can be in the order of thousands of km/hr, even though the average velocity of its molecules is zero.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Rotational energy    Rotational energy or angular kinetic energy is kinetic energy due to the rotation of an object and is part of its total kinetic energy. Looking at rotational energy separately around an object's axis of rotation, the following dependence on the object's moment of inertia is observed:

Erotational=12Iω2
where

ω is the angular velocity
I is the moment of inertia around the axis of rotation
E is the kinetic energy

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Rotational speed

Rotational speed (or speed of revolution) of an object rotating around an axis is the number of turns of the object divided by time, specified as revolutions per minute (rpm), cycles per second (cps), radians per second (rad/s), etc.[470] The symbol for rotational speed is ωcycLua error: Internal error: The interpreter has terminated with signal "24".(the Greek lowercase letter "omega"). Tangential speed v, rotational speed ωcyc, and radial distance r, are related by the following equation:[471]

v=2πrωcyc

v=rωrad
An algebraic rearrangement of this equation allows us to solve for rotational speed:

ωcyc=v/2πr

ωrad=v/r
Thus, the tangential speed will be directly proportional to r when all parts of a system simultaneously have the same ω, as for a wheel, disk, or rigid wand. The direct proportionality of v to r is not valid for the planets, because the planets have different rotational speeds (ω). Rotational speed can measure, for example, how fast a motor is running. Rotational speed and angular speed are sometimes used as synonyms, but typically they are measured with a different unit. Angular speed, however, tells the change in angle per time unit, which is measured in radians per second in the SI system. Since there are 2π radians per cycle, or 360 degrees per cycle, we can convert angular speed to rotational speed by

ωcyc=ωrad/2π
and

ωcyc=ωdeg/360
where

* ωcyc is rotational speed in cycles per second
* ωrad is angular speed in radians per second
* ωdeg is angular speed in degrees per second

For example, a stepper motor might turn exactly one complete revolution each second. Its angular speed is 360 degrees per second (360°/s), or 2π radians per second (2π rad/s), while the rotational speed is 60 rpm. Rotational speed is not to be confused with tangential speed, despite some relation between the two concepts. Imagine a rotating merry-go-round. No matter how close or far you stand from the axis of rotation, your rotational speed will remain constant. However, your tangential speed does not remain constant. If you stand two meters from the axis of rotation, your tangential speed will be double the amount if you were standing only one meter from the axis of rotation.

## S

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Safe failure fraction (SFF)    A term used in functional safety for the proportion of failures that are either non-hazardous or detected automatically. The opposite of SFF is the proportion of undetected, hazardous failures.[472]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Safety data sheet    A safety data sheet (SDS),[473] material safety data sheet (MSDS), or product safety data sheet (PSDS) are documents that list information relating to occupational safety and health for the use of various substances and products. SDSs are a widely used system for cataloguing information on chemicals, chemical compounds, and chemical mixtures. SDS information may include instructions for the safe use and potential hazards associated with a particular material or product, along with spill-handling procedures. The older MSDS formats could vary from source to source within a country depending on national requirements; however, the newer SDS format is internationally standardized.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Sanitary engineering    Sanitary engineering, also known as public health engineering or wastewater engineering, is the application of engineering methods to improve sanitation of human communities, primarily by providing the removal and disposal of human waste, and in addition to the supply of safe potable water.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Saturated compound    In chemistry, a saturated compound is a chemical compound (or ion) that resists the addition reactions, such as hydrogenation, oxidative addition, and binding of a Lewis base. The term is used in many contexts and for many classes of chemical compounds. Overall, saturated compounds are less reactive than unsaturated compounds. Saturation is derived from the Latin word saturare, meaning 'to fill')[474]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Scalar (mathematics)    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Scalar    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Scalar multiplication    In mathematics, scalar multiplication is one of the basic operations defining a vector space in linear algebra[475][476][477] (or more generally, a module in abstract algebra[478][479]). In common geometrical contexts, scalar multiplication of a real Euclidean vector by a positive real number multiplies the magnitude of the vector—without changing its direction. The term "scalar" itself derives from this usage: a scalar is that which scales vectors. Scalar multiplication is the multiplication of a vector by a scalar (where the product is a vector), and is to be distinguished from inner product of two vectors (where the product is a scalar).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Screw    A screw is a mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force.[480] It is one of the six classical simple machines. The most common form consists of a cylindrical shaft with helical grooves or ridges called threads around the outside.[481][482] The screw passes through a hole in another object or medium, with threads on the inside of the hole that mesh with the screw's threads. When the shaft of the screw is rotated relative to the stationary threads, the screw moves along its axis relative to the medium surrounding it; for example rotating a wood screw forces it into wood. In screw mechanisms, either the screw shaft can rotate through a threaded hole in a stationary object, or a threaded collar such as a nut can rotate around a stationary screw shaft.[483][484] Geometrically, a screw can be viewed as a narrow inclined plane wrapped around a cylinder.[480]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Series circuit    An electrical circuit in which the same current passes through each component, with only one path.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Servo    A motor that moves to and maintains a set position under command, rather than continuously moving.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Servomechanism    An automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Shadow matter    In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.[485]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Shear flow    The term shear flow is used in solid mechanics as well as in fluid dynamics. The expression shear flow is used to indicate:

* a shear stress over a distance in a thin-walled structure (in solid mechanics);[486]
* the flow induced by a force (in a fluid).

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Shear strength    Is the strength of a material or component against the type of yield or structural failure when the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is parallel to the direction of the force. When a paper is cut with scissors, the paper fails in shear. In structural and mechanical engineering, the shear strength of a component is important for designing the dimensions and materials to be used for the manufacture or construction of the component (e.g. beams, plates, or bolts). In a reinforced concrete beam, the main purpose of reinforcing bar (rebar) stirrups is to increase the shear strength.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Shear stress    Shear stress, often denoted by τ (Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. Normal stress, on the other hand, arises from the force vector component perpendicular to the material cross section on which it acts.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Shortwave radiation    Shortwave radiation (SW) is radiant energy with wavelengths in the visible (VIS), near-ultraviolet (UV), and near-infrared (NIR) spectra. There is no standard cut-off for the near-infrared range; therefore, the shortwave radiation range is also variously defined. It may be broadly defined to include all radiation with a wavelength of 0.1μm and 5.0μm or narrowly defined so as to include only radiation between 0.2μm and 3.0μm. There is little radiation flux (in terms of W/m2) to the Earth's surface below 0.2μm or above 3.0μm, although photon flux remains significant as far as 6.0μm, compared to shorter wavelength fluxes. UV-C radiation spans from 0.1μm to .28μm, UV-B from 0.28μm to 0.315μm, UV-A from 0.315μm to 0.4μm, the visible spectrum from 0.4μm to 0.7μm, and NIR arguably from 0.7μm to 5.0μm, beyond which the infrared is thermal.[487] Shortwave radiation is distinguished from longwave radiation. Downward shortwave radiation is sensitive to solar zenith angle, cloud cover.[488]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">SI units    The International System of Units (SI, abbreviated from the French Lua error: Internal error: The interpreter has terminated with signal "24".) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second (the unit of time with the symbol s), metre (length, m), kilogram (mass, kg), ampere (electric current, A), kelvin (thermodynamic temperature, K), mole (amount of substance, mol), and candela (luminous intensity, cd). The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units.[lower-alpha 7] Twenty-two derived units have been provided with special names and symbols.[lower-alpha 8] The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units,[lower-alpha 9] which are adopted to facilitate measurement of diverse quantities. The SI also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten (i.e. decimal) multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Signal processing    Is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as sound, images, and scientific measurements.[489] Signal processing techniques can be used to improve transmission, storage efficiency and subjective quality and to also emphasize or detect components of interest in a measured signal.[490]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Simple machine    Is a mechanical device that changes the direction or magnitude of a force.[491] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.[492] Usually the term refers to the six classical simple machines that were defined by Renaissance scientists:[493][494][495]

* Lever
* Wheel and axle
* Pulley
* Inclined plane
* Wedge
* Screw

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Siphon    A closed tube that conveys liquids between two levels without pumping.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Solid mechanics    Also known as mechanics of solids, is the branch of continuum mechanics that studies the behavior of solid materials, especially their motion and deformation under the action of forces, temperature changes, phase changes, and other external or internal agents.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Solid-state physics    Is the study of rigid matter, or solids, through methods such as quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state physics studies how the large-scale properties of solid materials result from their atomic-scale properties. Thus, solid-state physics forms a theoretical basis of materials science. It also has direct applications, for example in the technology of transistors and semiconductors.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Solid solution strengthening    Is a type of alloying that can be used to improve the strength of a pure metal.[328] The technique works by adding atoms of one element (the alloying element) to the crystalline lattice of another element (the base metal), forming a solid solution. The local nonuniformity in the lattice due to the alloying element makes plastic deformation more difficult by impeding dislocation motion through stress fields. In contrast, alloying beyond the solubility limit can form a second phase, leading to strengthening via other mechanisms (e.g. the precipitation of intermetallic compounds).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Solubility    Is the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and presence of other chemicals (including changes to the pH) of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Solubility equilibrium    Is a type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation or with chemical reaction with another constituent of the solution, such as acid or alkali. Each solubility equilibrium is characterized by a temperature-dependent solubility product which functions like an equilibrium constant. Solubility equilibria are important in pharmaceutical, environmental and many other scenarios.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Sound    In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Special relativity    In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates:[496][497][498]

1. The laws of physics are invariant (that is, identical) in all inertial frames of reference (that is, frames of reference with no acceleration).
2. The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Specific heat    The amount of energy required to change the temperature of a unit mass of substance by one degree.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Specific gravity    The ratio between the mass density of a substance to that of water.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Specific volume    The volume of a unit mass of a substance.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Specific weight    The weight of a substance per unit volume.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Spontaneous combustion    Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition.[499]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stagnation pressure    In fluid dynamics, stagnation pressure (or pitot pressure) is the static pressure at a stagnation point in a fluid flow.[500] At a stagnation point the fluid velocity is zero. In an incompressible flow, stagnation pressure is equal to the sum of the free-stream static pressure and the free-stream dynamic pressure.[501]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Standard electrode potential    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">State of matter    In physics, a state of matter is one of the distinct forms in which matter can exist. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many intermediate states are known to exist, such as liquid crystal, and some states only exist under extreme conditions, such as Bose–Einstein condensates, neutron-degenerate matter, and quark–gluon plasma, which only occur, respectively, in situations of extreme cold, extreme density, and extremely high energy. For a complete list of all exotic states of matter, see the list of states of matter.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Statics    The study of forces in a non-moving, rigid body.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Statistics    Is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data.[502][503][504] In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with a statistical population or a statistical model to be studied. Populations can be diverse groups of people or objects such as "all people living in a country" or "every atom composing a crystal". Statistics deals with every aspect of data, including the planning of data collection in terms of the design of surveys and experiments.[505]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Steam table    Thermodynamic data table containing steam or water properties .[506]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stefan–Boltzmann law    The Stefan–Boltzmann law describes the power radiated from a black body in terms of its temperature. Specifically, the Stefan–Boltzmann law states that the total energy radiated per unit surface area of a black body across all wavelengths per unit time j⋆ (also known as the black-body radiant emittance) is directly proportional to the fourth power of the black body's thermodynamic temperature T:

j⋆=σT4.
The constant of proportionality σ, called the Stefan–Boltzmann constant, is derived from other known physical constants. Since 2019, the value of the constant is

σ=2π5k415c2h3=5.670374…×10−8Wm−2K−4,
where k is the Boltzmann constant, h is Planck's constant, and c is the speed of light in a vacuum. The radiance from a specified angle of view (watts per square metre per steradian) is given by

L=j⋆π=σπT4.
A body that does not absorb all incident radiation (sometimes known as a grey body) emits less total energy than a black body and is characterized by an emissivity, ε<1:

j⋆=εσT4.
The radiant emittance j⋆ has dimensions of energy flux (energy per unit time per unit area), and the SI units of measure are joules per second per square metre, or equivalently, watts per square metre. The SI unit for absolute temperature T is the kelvin. ε is the emissivity of the grey body; if it is a perfect blackbody, ε=1. In the still more general (and realistic) case, the emissivity depends on the wavelength, ε=ε(λ). To find the total power radiated from an object, multiply by its surface area, A:

P=Aj⋆=AεσT4.
Wavelength- and subwavelength-scale particles,[507] metamaterials,[508] and other nanostructures are not subject to ray-optical limits and may be designed to exceed the Stefan–Boltzmann law.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stewart platform    Is a type of parallel manipulator that has six prismatic actuators, commonly hydraulic jacks or electric linear actuators, attached in pairs to three positions on the platform's baseplate, crossing over to three mounting points on a top plate. All 12 connections are made via universal joints. Devices placed on the top plate can be moved in the six degrees of freedom in which it is possible for a freely-suspended body to move: three linear movements x, y, z (lateral, longitudinal, and vertical), and the three rotations (pitch, roll, and yaw).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stiffness    Is the extent to which an object resists deformation in response to an applied force.[509] The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.[510]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stoichiometry    Refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers. This means that if the amounts of the separate reactants are known, then the amount of the product can be calculated. Conversely, if one reactant has a known quantity and the quantity of the products can be empirically determined, then the amount of the other reactants can also be calculated.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Strain    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Strain hardening    Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.[511] Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion.[512] Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at low temperatures, such as indium,[513] however others can be strengthened only via work hardening, such as pure copper and aluminum.[514]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Strength of materials    The field of strength of materials, also called mechanics of materials, typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the response of a structure under loading and its susceptibility to various failure modes takes into account the properties of the materials such as its yield strength, ultimate strength, Young's modulus, and Poisson's ratio. In addition, the mechanical element's macroscopic properties (geometric properties) such as its length, width, thickness, boundary constraints and abrupt changes in geometry such as holes are considered.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stress    In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighbouring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material. For example, when a solid vertical bar is supporting an overhead weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a closed container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface (such as a piston) push against them in (Newtonian) reaction. These macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Stress is frequently represented by a lowercase Greek letter sigma (σ).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stress–strain analysis    Stress–strain analysis (or stress analysis) is an engineering discipline that uses many methods to determine the stresses and strains in materials and structures subjected to forces. In continuum mechanics, stress is a physical quantity that expresses the internal forces that neighboring particles of a continuous material exert on each other, while strain is the measure of the deformation of the material. In simple terms we can define stress as the force of resistance per unit per unit area, offered by a body against deformation. Stress is the ratio of force over area (S =R/A, where S is the stress, R is the internal resisting force and A is the cross-sectional area). Strain is the ratio of change in length to the original length, when a given body is subjected to some external force (Strain= change in length÷the original length).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Stress–strain curve    In engineering and materials science, a stress–strain curve for a material gives the relationship between stress and strain. It is obtained by gradually applying load to a test coupon and measuring the deformation, from which the stress and strain can be determined (see tensile testing). These curves reveal many of the properties of a material, such as the Young's modulus, the yield strength and the ultimate tensile strength.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Structural analysis    Is the determination of the effects of loads on physical structures and their components. Structures subject to this type of analysis include all that must withstand loads, such as buildings, bridges, aircraft and ships. Structural analysis employs the fields of applied mechanics, materials science and applied mathematics to compute a structure's deformations, internal forces, stresses, support reactions, accelerations, and stability. The results of the analysis are used to verify a structure's fitness for use, often precluding physical tests. Structural analysis is thus a key part of the engineering design of structures.[515]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Structural load    A structural load or structural action is a force, deformation, or acceleration applied to structural elements.[516][517] A load causes stress, deformation, and displacement in a structure. Structural analysis, a discipline in engineering, analyzes the effects loads on structures and structural elements. Excess load may cause structural failure, so this should be considered and controlled during the design of a structure. Particular mechanical structures—such as aircraft, satellites, rockets, space stations, ships, and submarines—are subject to their own particular structural loads and actions.[518] Engineers often evaluate structural loads based upon published regulations, contracts, or specifications. Accepted technical standards are used for acceptance testing and inspection.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Sublimation    Is the transition of a substance directly from the solid to the gas state,[519] without passing through the liquid state.[520] Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point in its phase diagram, which corresponds to the lowest pressure at which the substance can exist as a liquid. The reverse process of sublimation is deposition or desublimation, in which a substance passes directly from a gas to a solid phase.[521] Sublimation has also been used as a generic term to describe a solid-to-gas transition (sublimation) followed by a gas-to-solid transition (deposition).[522] While vaporization from liquid to gas occurs as evaporation from the surface if it occurs below the boiling point of the liquid, and as boiling with formation of bubbles in the interior of the liquid if it occurs at the boiling point, there is no such distinction for the solid-to-gas transition which always occurs as sublimation from the surface.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Subsumption architecture    Is a reactive robotic architecture heavily associated with behavior-based robotics which was very popular in the 1980s and 90s. The term was introduced by Rodney Brooks and colleagues in 1986.[523][524][525] Subsumption has been widely influential in autonomous robotics and elsewhere in real-time AI.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Surface tension    Is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water to float on a water surface without becoming even partly submerged.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Superconductivity    Is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.[526][527][528][529]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Superhard material    Is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test.[530][531][532][533] They are virtually incompressible solids with high electron density and high bond covalency. As a result of their unique properties, these materials are of great interest in many industrial areas including, but not limited to, abrasives, polishing and cutting tools, disc brakes, and wear-resistant and protective coatings.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Supersaturation    Supersaturation occurs with a chemical solution when the concentration of a solute exceeds the concentration specified by the value equilibrium solubility. Most commonly the term is applied to a solution of a solid in a liquid. A supersaturated solution is in a metastable state; it may be brought to equilibrium by forcing the excess of solute to separate from the solution. The term can also be applied to a mixture of gases.

## T

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tangential acceleration    The velocity of a particle moving on a curved path as a function of time can be written as:

𝐯(t)=v(t)𝐯(t)v(t)=v(t)𝐮t(t),
with v(t) equal to the speed of travel along the path, and

𝐮t=𝐯(t)v(t) ,
a unit vector tangent to the path pointing in the direction of motion at the chosen moment in time. Taking into account both the changing speed v(t) and the changing direction of ut, the acceleration of a particle moving on a curved path can be written using the chain rule of differentiation[534] for the product of two functions of time as:

𝐚=d𝐯dt=dvdt𝐮t+v(t)d𝐮tdt=dvdt𝐮t+v2r𝐮n ,
where un is the unit (inward) normal vector to the particle's trajectory (also called the principal normal), and r is its instantaneous radius of curvature based upon the osculating circle at time t. These components are called the tangential acceleration and the normal or radial acceleration (or centripetal acceleration in circular motion, see also circular motion and centripetal force). Geometrical analysis of three-dimensional space curves, which explains tangent, (principal) normal and binormal, is described by the Frenet–Serret formulas.[535][536]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Technical standard    A technical standard is an established norm or requirement for a repeatable technical task. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes, and practices. In contrast, a custom, convention, company product, corporate standard, and so forth that becomes generally accepted and dominant is often called a de facto standard.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Temperature    Is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source of the occurrence of heat, a flow of energy, when a body is in contact with another that is colder. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have used various reference points and thermometric substances for definition. The most common scales are the Celsius scale (formerly called centigrade, denoted °C), the Fahrenheit scale (denoted °F), and the Kelvin scale (denoted K), the last of which is predominantly used for scientific purposes by conventions of the International System of Units (SI).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tempering (metallurgy)    Heat treatment to alter the crystal structure of a metal such as steel.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tensile force    Pulling force, tending to lengthen an object.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tensile modulus    Young's modulus E, the Young modulus, or the modulus of elasticity in tension, is a mechanical property that measures the tensile stiffness of a solid material. It quantifies the relationship between tensile stress σ (force per unit area) and axial strain ε (proportional deformation) in the linear elastic region of a material and is determined using the formula:[537] E=σε Young's moduli are typically so large that they are expressed not in pascals but in gigapascals (GPa).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tensile strength    Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or Ftu within equations,[538][539][540] is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials the ultimate tensile strength is close to the yield point, whereas in ductile materials the ultimate tensile strength can be higher.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tensile testing    Tensile testing, also known as tension testing,[541] is a fundamental materials science and engineering test in which a sample is subjected to a controlled tension until failure. Properties that are directly measured via a tensile test are ultimate tensile strength, breaking strength, maximum elongation and reduction in area.[542] From these measurements the following properties can also be determined: Young's modulus, Poisson's ratio, yield strength, and strain-hardening characteristics.[543] Uniaxial tensile testing is the most commonly used for obtaining the mechanical characteristics of isotropic materials. Some materials use biaxial tensile testing. The main difference between these testing machines being how load is applied on the materials.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Tension member    Tension members are structural elements that are subjected to axial tensile forces. Examples of tension members are bracing for buildings and bridges, truss members, and cables in suspended roof systems.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Thermal conduction    Is the transfer of internal energy by microscopic collisions of particles and movement of electrons within a body. The colliding particles, which include molecules, atoms and electrons, transfer disorganized microscopic kinetic and potential energy, jointly known as internal energy. Conduction takes place in all phases: solid, liquid, and gas.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Thermal equilibrium    Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in thermal equilibrium with itself if the temperature within the system is spatially uniform and temporally constant. Systems in thermodynamic equilibrium are always in thermal equilibrium, but the converse is not always true. If the connection between the systems allows transfer of energy as 'change in internal energy' but does not allow transfer of matter or transfer of energy as work, the two systems may reach thermal equilibrium without reaching thermodynamic equilibrium.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Thermal radiation    Is electromagnetic radiation generated by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Thermodynamics    Is a branch of physics that deals with heat, work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed by the four laws of thermodynamics which convey a quantitative description using measurable macroscopic physical quantities, but may be explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, biochemistry, chemical engineering and mechanical engineering, but also in other complex fields such as meteorology.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Theory of relativity    Usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively.[544] Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to other forces of nature.[545] It applies to the cosmological and astrophysical realm, including astronomy.[546]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Thévenin's theorem    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Three-phase electric power    Is a common method of alternating current electric power generation, transmission, and distribution.[547] It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Torque    Twisting force.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Torsional vibration    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Toughness    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Trajectory    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Transducer    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Transformer    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Trigonometric functions    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Trigonometry    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Trimean    The trimean is a measure of a probability distribution's location defined as a weighted average of the distribution's median and its two quartiles
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Triple point    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Trouton's rule    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Truncated mean    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Truss    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Turbine    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Turbomachinery    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Turbulence    .

## U

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Ultimate tensile strength    Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or Ftu within equations,[538][539][540] is the capacity of a material or structure to withstand loads tending to elongate, as opposed to compressive strength, which withstands loads tending to reduce size. In other words, tensile strength resists tension (being pulled apart), whereas compressive strength resists compression (being pushed together). Ultimate tensile strength is measured by the maximum stress that a material can withstand while being stretched or pulled before breaking. In the study of strength of materials, tensile strength, compressive strength, and shear strength can be analyzed independently.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Uncertainty principle    In quantum mechanics, the uncertainty principle (also known as Heisenberg's uncertainty principle) is any of a variety of mathematical inequalities[548] asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables, such as position x and momentum p, can be known.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Unicode    A standard for the consistent encoding of textual characters.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Unit vector    In mathematics, a unit vector in a normed vector space is a vector (often a spatial vector) of length 1\. A unit vector is often denoted by a lowercase letter with a circumflex, or "hat": ı^ (pronounced "i-hat"). The term direction vector is used to describe a unit vector being used to represent spatial direction, and such quantities are commonly denoted as d. .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Unsaturated compound    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Upthrust    Buoyancy, or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and (as explained by Archimedes' principle) is equivalent to the weight of the fluid that would otherwise occupy the submerged volume of the object, i.e. the displaced fluid.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Utility frequency    The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country.

## V

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Vacuole    Is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal[549] and bacterial cells.[550] Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these.[551] The organelle has no basic shape or size; its structure varies according to the requirements of the cell.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Vacuum    An absence of mass in a volume.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valence    In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of valence developed in the second half of the 19th century and helped successfully explain the molecular structure of inorganic and organic compounds.[552] The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valence band    In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level and thus determine the electrical conductivity of the solid. In non-metals, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a material, the valence band is located below the Fermi level, while the conduction band is located above it. The distinction between the valence and conduction bands is meaningless in metals, because conduction occurs in one or more partially filled bands that take on the properties of both the valence and conduction bands.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valence bond theory    In chemistry, valence bond (VB) theory is one of the two basic theories, along with molecular orbital (MO) theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds when a molecule is formed. In contrast, molecular orbital theory has orbitals that cover the whole molecule.[553]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valence electron    In chemistry and physics, a valence electron is an outer shell electron that is associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valence shell    The valence shell is the set of orbitals which are energetically accessible for accepting electrons to form chemical bonds. For main group elements, the valence shell consists of the ns and np orbitals in the outermost electron shell. In the case of transition metals (the (n-1)d orbitals), and lanthanides and actinides (the (n-2)f and (n-1)d orbitals), the orbitals involved can also be in an inner electron shell. Thus, the shell terminology is a misnomer as there is no correspondence between the valence shell and any particular electron shell in a given element. A scientifically correct term would be valence orbital to refer to the energetically accessible orbitals of an element.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Valve    Is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">van der Waals equation    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">van der Waals force    In molecular physics, the Van der Waals force, named after Dutch physicist Johannes Diderik van der Waals, is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and therefore more susceptible to disturbance. The Van der Waals force quickly vanishes at longer distances between interacting molecules.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">van 't Hoff equation    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">van 't Hoff factor    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Variable capacitor    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Variable resistor    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Vector space    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Venturi effect    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Vibration    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Virtual leak    Traces of gas trapped in cavities within a vacuum chamber, slowly dissipating out in the main chamber, thus appearing like a leak from the outside.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Viscoelasticity    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Viscosity    The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or tensile stress.[554] For liquids, it corresponds to the informal concept of "thickness": for example, honey has a higher viscosity than water.[555]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Volt-ampere    (VA), is the unit used for the apparent power in an electrical circuit. The apparent power equals the product of root-mean-square (RMS) voltage and RMS current.[556] In direct current (DC) circuits, this product is equal to the real power (active power)[557] in watts. Volt-amperes are useful only in the context of alternating current (AC) circuits. The volt-ampere is dimensionally equivalent to the watt (in SI units, 1 VA = 1 N m A−1 s −1 A = 1 N m s −1 = 1 J s −1 = 1 W). VA rating is most useful in rating wires and switches (and other power handling equipment) for inductive loads.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Volt-ampere reactive    .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Volta potential    The Volta potential (also called Volta potential difference, contact potential difference, outer potential difference, Δψ, or "delta psi") in electrochemistry, is the electrostatic potential difference between two metals (or one metal and one electrolyte) that are in contact and are in thermodynamic equilibrium. Specifically, it is the potential difference between a point close to the surface of the first metal, and a point close to the surface of the second metal (or electrolyte).[558]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Voltage    Voltage, electric potential difference, electric pressure  or electric tension is the difference in electric potential between two points. The difference in electric potential between two points (i.e., voltage) is defined as the work needed per unit of charge against a static electric field to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named volt.[559] In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The official SI definition for volt uses power and current, where 1 volt = 1 watt (of power) per 1 ampere (of current).[559]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Volumetric flow rate    Also known as volume flow rate, rate of fluid flow or volume velocity, is the volume of fluid which passes per unit time; usually represented by the symbol Q (sometimes V̇). The SI unit is m3/s (cubic metres per second).
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">von Mises yield criterion    The von Mises yield criterion (also known as the maximum distortion energy criterion[560]) suggests that yielding of a ductile material begins when the second deviatoric stress invariant J2 reaches a critical value.[561] It is part of plasticity theory that applies best to ductile materials, such as some metals. Prior to yield, material response can be assumed to be of a nonlinear elastic, viscoelastic, or linear elastic behavior. In materials science and engineering the von Mises yield criterion can also be formulated in terms of the von Mises stress or equivalent tensile stress, σv. This is a scalar value of stress that can be computed from the Cauchy stress tensor. In this case, a material is said to start yielding when the von Mises stress reaches a value known as yield strength, σy. The von Mises stress is used to predict yielding of materials under complex loading from the results of uniaxial tensile tests. The von Mises stress satisfies the property where two stress states with equal distortion energy have an equal von Mises stress.

## W

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Watt    The SI unit of power, rate of doing work.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Wave    Is a disturbance that transfers energy through matter or space, with little or no associated mass transport. Waves consist of oscillations or vibrations of a physical medium or a field, around relatively fixed locations. From the perspective of mathematics, waves, as functions of time and space, are a class of signals.[562]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Wavelength    Is the spatial period of a periodic wave—the distance over which the wave's shape repeats.[563][564] It is thus the inverse of the spatial frequency. Wavelength is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns.[565][566] Wavelength is commonly designated by the Greek letter lambda (λ). The term wavelength is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids.[567]' .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Wedge    Is a triangular shaped tool, and is a portable inclined plane, and one of the six classical simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by converting a force applied to its blunt end into forces perpendicular (normal) to its inclined surfaces. The mechanical advantage of a wedge is given by the ratio of the length of its slope to its width.[568][569] Although a short wedge with a wide angle may do a job faster, it requires more force than a long wedge with a narrow angle.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Weighted arithmetic mean    The weighted arithmetic mean is similar to an ordinary arithmetic mean (the most common type of average), except that instead of each of the data points contributing equally to the final average, some data points contribute more than others. The notion of weighted mean plays a role in descriptive statistics and also occurs in a more general form in several other areas of mathematics. If all the weights are equal, then the weighted mean is the same as the arithmetic mean. While weighted means generally behave in a similar fashion to arithmetic means, they do have a few counterintuitive properties, as captured for instance in Simpson's paradox.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Wet-bulb temperature    The temperature of a wetted thermometer with an air current across it. Used in psychrometry. .
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Wheel and axle    Are one of six simple machines identified by Renaissance scientists drawing from Greek texts on technology.[570] The wheel and axle consists of a wheel attached to a smaller axle so that these two parts rotate together in which a force is transferred from one to the other. A hinge or bearing supports the axle, allowing rotation. It can amplify force; a small force applied to the periphery of the large wheel can move a larger load attached to the axle.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Winsorized mean    Is a winsorized statistical measure of central tendency, much like the mean and median, and even more similar to the truncated mean. It involves the calculation of the mean after replacing given parts of a probability distribution or sample at the high and low end with the most extreme remaining values,[571] typically doing so for an equal amount of both extremes; often 10 to 25 percent of the ends are replaced. The winsorized mean can equivalently be expressed as a weighted average of the truncated mean and the quantiles at which it is limited, which corresponds to replacing parts with the corresponding quantiles.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Work hardening    Also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.[572]

## X

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">X-axis    In algebraic geometry, the axis on a graph that is usually drawn left to right and usually shows the range of values of an independent variable.[573]

## Y

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Y-axis    In algebraic geometry, the axis on a graph that is usually drawn from bottom to top and usually shows the range of values of variable dependent on one other variable, or the second of two independent variables.[574]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Yield    The point of maximum elastic deformation of a material; above yield the material is permanently deformed.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Young's modulus    A measure of the stiffness of a material; the amount of force per unit area require to produce a unit strain.

## Z

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Z-axis    In algebraic geometry, the axis on a graph of at least three dimensions that is usually drawn vertically and usually shows the range of values of a variable dependent on two other variables or the third independent variable.[575]
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Zero defects    A quality assurance philosophy that aims to reduce the need for inspection of components by improving their quality.
<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Zero force member    In the field of engineering mechanics, a zero force member is a member (a single truss segment) in a truss which, given a specific load, is at rest: neither in tension, nor in compression. In a truss a zero force member is often found at pins (any connections within the truss) where no external load is applied and three or fewer truss members meet. Recognizing basic zero force members can be accomplished by analyzing the forces acting on an individual pin in a physical system. NOTE: If the pin has an external force or moment applied to it, then all of the members attached to that pin are not zero force members UNLESS the external force acts in a manner that fulfills one of the rules below:

* If two non-collinear members meet in an unloaded joint, both are zero-force members.
* If three members meet in an unloaded joint of which two are collinear, then the third member is a zero-force member.

Reasons for Zero-force members in a truss system

* These members contribute to the stability of the structure, by providing buckling prevention for long slender members under compressive forces
* These members can carry loads in the event that variations are introduced in the normal external loading configuration.

<dt class="glossary " id="Lua error: Internal error: The interpreter has terminated with signal "24"." style="margin-top: 0.4em;">Zeroth law of thermodynamics    The equivalence principle applied to temperature; two systems in thermal equiplbirum with a third are also in thermal equilibrium with each other.

## See also

* Engineering
* National Council of Examiners for Engineering and Surveying
* Fundamentals of Engineering Examination
* Principles and Practice of Engineering Examination
* Graduate Aptitude Test in Engineering
* Glossary of aerospace engineering
* Glossary of civil engineering
* Glossary of electrical and electronics engineering
* Glossary of mechanical engineering
* Glossary of structural engineering
* Glossary of architecture
* Glossary of areas of mathematics
* Glossary of artificial intelligence
* Glossary of astronomy
* Glossary of biology
* Glossary of calculus
* Glossary of chemistry
* Glossary of ecology
* Glossary of economics
* Glossary of physics
* Glossary of probability and statistics
* Lua error: Internal error: The interpreter has terminated with signal "24".

## Notes

1. ↑ The second law of thermodynamics imposes limitations on the capacity of a system to transfer energy by performing work, since some of the system's energy might necessarily be consumed in the form of heat instead. See e.g. Lehrman, Robert L. (1973). "Energy Is Not The Ability To Do Work". The Physics Teacher 11 (1): 15–18. doi:10.1119/1.2349846. ISSN 0031-921X. Bibcode: 1973PhTea..11...15L.
2. ↑ The words map, mapping, transformation, correspondence, and operator are often used synonymously. Lua error: Internal error: The interpreter has terminated with signal "24"..
3. ↑ Electric and magnetic fields, according to the theory of relativity, are the components of a single electromagnetic field.
4. ↑ Pronounced "x bar".
5. ↑ Greek letter μ, for "mean", pronounced /'mjuː/.
6. ↑ Strictly speaking, a probability of 0 indicates that an event almost never takes place, whereas a probability of 1 indicates than an event almost certainly takes place. This is an important distinction when the sample space is infinite. For example, for the continuous uniform distribution on the real interval [5, 10], there are an infinite number of possible outcomes, and the probability of any given outcome being observed — for instance, exactly 7 — is 0. This means that when we make an observation, it will almost surely not be exactly 7. However, it does not mean that exactly 7 is impossible. Ultimately some specific outcome (with probability 0) will be observed, and one possibility for that specific outcome is exactly 7.

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1. ↑ "Newtonian constant of gravitation" is the name introduced for G by Boys (1894). Use of the term by T.E. Stern (1928) was misquoted as "Newton's constant of gravitation" in Pure Science Reviewed for Profound and Unsophisticated Students (1930), in what is apparently the first use of that term. Use of "Newton's constant" (without specifying "gravitation" or "gravity") is more recent, as "Newton's constant" was also used for the heat transfer coefficient in Newton's law of cooling, but has by now become quite common, e.g. Calmet et al, Quantum Black Holes (2013), p. 93; P. de Aquino, Beyond Standard Model Phenomenology at the LHC (2013), p. 3. The name "Cavendish gravitational constant", sometimes "Newton–Cavendish gravitational constant", appears to have been common in the 1970s to 1980s, especially in (translations from) Soviet-era Russian literature, e.g. Sagitov (1970 [1969]), Soviet Physics: Uspekhi 30 (1987), Issues 1–6, p. 342 [etc.]. "Cavendish constant" and "Cavendish gravitational constant" is also used in Charles W. Misner, Kip S. Thorne, John Archibald Wheeler, "Gravitation", (1973), 1126f. Colloquial use of "Big G", as opposed to "little g" for gravitational acceleration dates to the 1960s (R.W. Fairbridge, The encyclopedia of atmospheric sciences and astrogeology, 1967, p. 436; note use of "Big G's" vs. "little g's" as early as the 1940s of the Einstein tensor Gμν vs. the metric tensor gμν, Scientific, medical, and technical books published in the United States of America: a selected list of titles in print with annotations: supplement of books published 1945–1948, Committee on American Scientific and Technical Bibliography National Research Council, 1950, p. 26).
2. ↑ Integral calculus is a very well established mathematical discipline for which there are many sources. See Lua error: Internal error: The interpreter has terminated with signal "24". and Lua error: Internal error: The interpreter has terminated with signal "24"., for example.
3. ↑ The photon's invariant mass (also called "rest mass" for massive particles) is believed to be exactly zero. This is the notion of particle mass generally used by modern physicists. The photon does have a nonzero relativistic mass, depending on its energy, but this varies according to the frame of reference.
4. ↑ At the start of The Feynman Lectures on Physics, Richard Feynman offers the atomic hypothesis as the single most prolific scientific concept.[431]
5. ↑ The term "universe" is defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term "universe" may also be used in slightly different contextual senses, denoting concepts such as the cosmos or the philosophical world.
6. ↑ The preferred spelling varies by country and even by industry. Further, both spellings are often used within a particular industry or country. Industries in British English-speaking countries typically use the "gauge" spelling.
7. ↑ For example, the SI unit of velocity is the metre per second, m⋅s−1; of acceleration is the metre per second squared, m⋅s−2; etc.
8. ↑ For example the newton (N), the unit of force, equivalent to kg⋅m⋅s−2; the joule (J), the unit of energy, equivalent to kg⋅m2⋅s−2, etc. The most recently named derived unit, the katal, was defined in 1999.
9. ↑ For example, the recommended unit for the electric field strength is the volt per metre, V/m, where the volt is the derived unit for electric potential difference. The volt per metre is equal to kg⋅m⋅s−3⋅A−1 when expressed in terms of base units.

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Lua error: Internal error: The interpreter has terminated with signal "24".

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1. ↑ For example, the SI unit of velocity is the metre per second, m⋅s−1; of acceleration is the metre per second squared, m⋅s−2; etc.
2. ↑ For example the newton (N), the unit of force, equivalent to kg⋅m⋅s−2; the joule (J), the unit of energy, equivalent to kg⋅m2⋅s−2, etc. The most recently named derived unit, the katal, was defined in 1999.
3. ↑ For example, the recommended unit for the electric field strength is the volt per metre, V/m, where the volt is the derived unit for electric potential difference. The volt per metre is equal to kg⋅m⋅s−3⋅A−1 when expressed in terms of base units.

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## References

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