Glossary 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.

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 C_nH_2n−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 [math]\displaystyle{ I }[/math] for an axis that lies in the plane or with a [math]\displaystyle{ J }[/math] 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:

[math]\displaystyle{ y'+ P(x)y = Q(x)y^n\, }[/math]

is called a Bernoulli differential equation where [math]\displaystyle{ n }[/math] is any real number and [math]\displaystyle{ n \ne 0 }[/math] and [math]\displaystyle{ n \ne 1 }[/math].^[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](§ 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 (k_B 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 N_A:

[math]\displaystyle{ k = \frac{R}{N_\text{A}} . }[/math].

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,

[math]\displaystyle{ \frac{\mathrm{d}P}{\mathrm{d}T} = \frac{L}{T\,\Delta v}=\frac{\Delta s}{\Delta v}, }[/math]

where [math]\displaystyle{ \mathrm{d}P/\mathrm{d}T }[/math] is the slope of the tangent to the coexistence curve at any point, [math]\displaystyle{ L }[/math] is the specific latent heat, [math]\displaystyle{ T }[/math] is the temperature, [math]\displaystyle{ \Delta v }[/math] is the specific volume change of the phase transition, and [math]\displaystyle{ \Delta s }[/math] 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,

[math]\displaystyle{ \oint \frac{\delta Q}{T_{surr}} \leq 0, }[/math]

where [math]\displaystyle{ \delta Q }[/math] is the infinitesimal amount of heat absorbed by the system from the reservoir and [math]\displaystyle{ T_{surr} }[/math] 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]

[math]\displaystyle{ dS \gt \frac{\delta Q}{T_{surr}} }[/math]

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 [math]\displaystyle{ \ \sigma }[/math] to the mean [math]\displaystyle{ \ \mu }[/math] (or its absolute value, [math]\displaystyle{ | \mu | }[/math]).

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.

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] .

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.

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.

Cosmic rays

Cosmic rays are high-energy radiation, mainly originating outside the Solar System.^[138]

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:

[math]\displaystyle{ 1 ~ \text{C} = 1 ~ \text{A} \cdot 1 ~ \text{s} }[/math]

Thus, it is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:

[math]\displaystyle{ 1 ~ \text{C} = 1 ~ \text{F} \cdot 1 ~ \text{V} }[/math]

The coulomb is equivalent to the charge of approximately 6.242×10¹⁸ (1.036×10⁻⁵ mol) protons, and −1 C is equivalent to the charge of approximately 6.242×10¹⁸ 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 1.602176634×10⁻¹⁹ coulombs. This would implicitly define the coulomb as ​¹⁄_0.1602176634×10¹⁸ elementary charges.

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:

[math]\displaystyle{ F=k_e\frac{q_1 q_2}{r^2} }[/math],

where k_e is Coulomb's constant (k_e ≈ 9×10⁹ N m² C⁻²), 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.

Covalent bond

A covalent bond, also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms.

Crookes tube

A type of vacuum tube that demonstrates cathode rays.

Cryogenics

The science of low temperatures.

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.

Crystallography

The study of crystals.

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.

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

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]

Damped vibration

Any vibration with a force acting against it to lessen the vibration over time.

Darcy–Weisbach equation

An equation used in fluid mechanics to find the pressure change cause by friction within a pipe or conduit.

DC motor

An electrical motor driven by direct current.

Decibel

A logarithmic unit of ratios.

Definite integral

The integral of a function between an upper and lower limit.^[149]

Deflection

Is the degree to which a structural element is displaced under a load. It may refer to an angle or a distance.

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]

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.

Degrees of freedom

The number of parameters required to define the motion of a dynamical system.

Delta robot

A tripod linkage, used to construct fast-acting manipulators with a wide range of movement.

Delta-wye transformer

A type of transformer used in three-phase power systems.

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 [math]\displaystyle{ n }[/math] independent Bernoulli trials, each having probability [math]\displaystyle{ p }[/math] of success (a binomial distribution with [math]\displaystyle{ n }[/math] trials), converges to the probability density function of the normal distribution with mean [math]\displaystyle{ np }[/math] and standard deviation[math]\displaystyle{ \sqrt{np(1-p)} }[/math], as [math]\displaystyle{ n }[/math] grows large, assuming [math]\displaystyle{ p }[/math] is not [math]\displaystyle{ 0 }[/math] or [math]\displaystyle{ 1 }[/math].

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]

[math]\displaystyle{ \rho = \frac{m}{V} }[/math]

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.

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.

Design engineering

.

Dew point

The pressure and temperature at which air is holding the maximum possible humidity.

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.

Dielectric

An insulator, a material that does not permit free flow of electricity.

Differential pressure

.

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]

Differential signaling

Is a method for electrically transmitting information using two complementary signals.

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).

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]}

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 [math]\displaystyle{ w(x) }[/math], taking downward to be positive, the internal shear force is given by taking the negative integral of the weight:

[math]\displaystyle{ V(x) = -\int w(x)\, dx }[/math]

The internal moment M(x) is the integral of the internal shear:

[math]\displaystyle{ M(x) = \int V(x)\, dx }[/math] = [math]\displaystyle{ -\int [\int w(x)\ \, dx] dx }[/math]

The angle of rotation from the horizontal, [math]\displaystyle{ \theta }[/math], is the integral of the internal moment divided by the product of the Young's modulus and the area moment of inertia:

[math]\displaystyle{ \theta (x) = \frac{1}{EI} \int M(x)\, dx }[/math]

Integrating the angle of rotation obtains the vertical displacement [math]\displaystyle{ \nu }[/math]:

[math]\displaystyle{ \nu (x) = \int \theta (x) dx }[/math].

E

Economics

The scientific study of the production, distribution and consumption of goods.

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]

Elastic modulus

The amount a material will deform per unit force.

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.

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.

Electric circuit

Is an electrical network consisting of a closed loop, giving a return path for the current.

Electric current

Is a flow of electric charge.^[169]:2 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]

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).

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.

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.

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.

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.

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.

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.

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.

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. .

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).

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.

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.

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.

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.

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).

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.

Electrodynamics

In physics, the phenomena associated with moving electric charges, and their interaction with electric and magnetic fields; the study of these phenomena.^[174]

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.

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.)

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]

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.

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.

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 1.602176634×10⁻¹⁹ J.^[186]

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]

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.

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.

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.

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.

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.

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]

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]

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.

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.

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]}

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]:8.1

Escape velocity

The minimum velocity at which an object can escape a gravitation field.

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).

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.

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

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.

Falling bodies

.

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.

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

96485.33212... C mol⁻¹.^[210]

This constant has a simple relation to two other physical constants:

[math]\displaystyle{ F\,=\,eN_{A} }[/math]

where

e = 1.602176634×10⁻¹⁹ C;^[211]

N_A = 6.02214076×10²³ mol⁻¹.^[212]

Both of these values have exact defined values, and hence F has a known exact value. N_A 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.

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.

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.

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.

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.

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.

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).

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.

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).

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.

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]

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.

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.

Foot-pound

The foot-pound force (symbol: ft⋅lbf,^[221] ft⋅lb_f,^[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.

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 [math]\displaystyle{ K_\text{Ic} }[/math].^[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 [math]\displaystyle{ K_\text{c} }[/math]. 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.

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.

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.

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.

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]

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]

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.

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.)

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]}

Fundamental theorem of calculus

Is a theorem that links the concept of differentiating a function with the concept of integrating a function.

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

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]

Gamma rays

A gamma ray, or gamma radiation (symbol γ or [math]\displaystyle{ \gamma }[/math]), 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.

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.

Gauge pressure

Is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure.

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.

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.

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, ..., x_n, the geometric mean is defined as

[math]\displaystyle{ \left(\prod_{i=1}^n x_i\right)^\frac{1}{n} = \sqrt[n]{x_1 x_2 \cdots x_n} }[/math]

H

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.

Haptic

Tactile feedback technology using the operator's sense of touch. Also sometimes applied to robot manipulators with their own touch sensitivity.

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.

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

[math]\displaystyle{ \left(\frac{1^{-1} + 4^{-1} + 4^{-1}}{3}\right)^{-1} = \frac{3}{\frac{1}{1} + \frac{1}{4} + \frac{1}{4}} = \frac{3}{1.5} = 2\,. }[/math]

I

Ice point

The freezing point of pure water at one atmosphere; 0°C (32°F).^[274]

Ideal gas

A model for gases that ignores inter-molecular forces. Most gases are approximately ideal at some high temperature and low pressure.

Ideal gas constant

The constant in the gas law that relates pressure, volume and temperature.

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:

[math]\displaystyle{ PV = nRT }[/math]

where [math]\displaystyle{ P }[/math], [math]\displaystyle{ V }[/math] and [math]\displaystyle{ T }[/math] are the pressure, volume and temperature; [math]\displaystyle{ n }[/math] is the amount of substance; and [math]\displaystyle{ R }[/math] 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]

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, [math]\displaystyle{ (a+b)^2 = a^2 + 2ab + b^2 }[/math] and [math]\displaystyle{ \cos^2\theta + \sin^2\theta =1 }[/math] are identities.^[280] Identities are sometimes indicated by the triple bar symbol ≡ instead of =, the equals sign.^[281]

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.

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]

Indefinite integral

A function whose derivative is a given function; an antiderivative.^[285]

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.

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.

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]

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.

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.

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.

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.

International System of Units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) 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.

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.

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]

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.

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.

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.

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

J/psi meson

The J/ψ (J/psi) meson /ˈdʒeɪ ˈsaɪ ˈmiːzɒn/ 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 3.0969 GeV/c², just above that of the η_c (2.9836 GeV/c²), and a mean lifetime of 7.2×10⁻²¹ s. This lifetime was about a thousand times longer than expected.^[294]

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.

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

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.

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).

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]

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

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.

Laplace transform

In mathematics, the Laplace transform, named after its inventor Pierre-Simon Laplace (/ləˈplɑːs/), is an integral transform that converts a function of a real variable [math]\displaystyle{ t }[/math] (often time) to a function of a complex variable [math]\displaystyle{ s }[/math] (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]}

LC circuit

A circuit consisting entirely of inductors (L) and capacitors (C).

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.

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]

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.

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.

L'Hôpital's rule

In mathematics, more specifically calculus, L'Hôpital's rule or L'Hospital's rule (French: [lopital], English: /ˌloʊpiːˈtɑːl/, loh-pee-TAHL) 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 [math]\displaystyle{ \lim_{x\to c}f(x)=\lim_{x\to c}g(x)=0 \text{ or } \pm\infty, }[/math] and [math]\displaystyle{ g'(x)\ne 0 }[/math] for all x in I with x ≠ c, and [math]\displaystyle{ \lim_{x\to c}\frac{f'(x)}{g'(x)} }[/math] exists, then

[math]\displaystyle{ \lim_{x\to c}\frac{f(x)}{g(x)} = \lim_{x\to c}\frac{f'(x)}{g'(x)}. }[/math]

The differentiation of the numerator and denominator often simplifies the quotient or converts it to a limit that can be evaluated directly.

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).

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.

Linear algebra

The mathematics of equations where the unknowns are only in the first power.

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.

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.

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 log_b(x), or without parentheses, log_b 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 log_b(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:

[math]\displaystyle{ \log_b(x) = y \ }[/math] exactly if [math]\displaystyle{ \ b^y = x\ }[/math] and [math]\displaystyle{ \ x \gt 0 }[/math] and [math]\displaystyle{ \ b \gt 0 }[/math] and [math]\displaystyle{ \ b \ne 1 }[/math].

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]

Logarithmic identities

Several important formulas, sometimes called logarithmic identities or log laws, relate logarithms to one another.^[318]

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.

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.

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

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.

Mach number

The ratio of the speed of an object to the speed of sound.

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.

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.

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]

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]

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.

Magnetic field

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents,^{[326]:ch1[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]:ch13[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, [math]\displaystyle{ \mathbf{B}/\mu_0 = \mathbf{H} }[/math]; but in a magnetized material, the terms differ by the material's magnetization at each point.

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.

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.

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]:59–62}

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]

[math]\displaystyle{ \rho = \frac{m}{V} }[/math]

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.

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.

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 ¹²C, 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]

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.

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.

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.

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.

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.

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]

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.

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,

[math]\displaystyle{ \begin{bmatrix}1 & 9 & -13 \\20 & 5 & -6 \end{bmatrix} }[/math]

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]

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]:21[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]

Maximum-distortion energy theory

.

Maximum-normal-stress theory

.

Maximum shear stress

.

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.

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, ..., x_n is typically denoted by [math]\displaystyle{ \bar{x} }[/math]^{[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 [math]\displaystyle{ \bar{x} }[/math]) to distinguish it from the mean, or expected value, of the underlying distribution, the population mean (denoted [math]\displaystyle{ \mu }[/math] or [math]\displaystyle{ \mu_x }[/math]^{[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 [math]\displaystyle{ \mu = \sum x p(x).... }[/math].^[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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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]

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.

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).

Middle-out

A combination of top-down and bottom-up design.^[378]

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:^[379]

[math]\displaystyle{ M=\frac{\max x + \min x}{2}. }[/math]

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.

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.

[math]\displaystyle{ \operatorname{MH}(X) = \overline{Q_{1, 3}(X)} = \frac{Q_1(X) + Q_3(X)}{2} = \frac{P_{25}(X) + P_{75}(X)}{2} = M_{25}(X) }[/math]

The midhinge is related to the interquartile range (IQR), the difference of the third and first quartiles (i.e. [math]\displaystyle{ IQR = Q_3 - Q_1 }[/math]), 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,^[380] and "midhinge" is a fairly modern term dating from around that time. The midhinge is slightly simpler to calculate than the trimean ([math]\displaystyle{ TM }[/math]), which originated in the same context and equals the average of the median ([math]\displaystyle{ \tilde{X} = Q_2 = P_{50} }[/math]) and the midhinge.

[math]\displaystyle{ \operatorname{MH}(X) = 2 \operatorname{TM}(X) - \operatorname{med}(X) = 2 \frac{Q_1 + 2Q_2 + Q3}{4} - Q_2 }[/math]

N

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.

Nanotechnology

The technology of systems built with moving parts on the order of a nanometre in size.

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.

Neutrino

A neutrino (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1/2) that interacts only via the weak subatomic force and gravity.^[402][403] 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.^[404] The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction.^[405] Thus, neutrinos typically pass through normal matter unimpeded and undetected.^[406][403]

Newtonian fluid

Is a fluid in which the viscous stresses arising from its flow, at every point, are linearly^[407] correlated to the local strain rate—the rate of change of its deformation over time.^{[408][409][410]} 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.

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.

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.

nth root

To put a number of function to the exponential power of 1/n.

Nuclear binding energy

The difference between the total mass energy of a nucleus and the mass energy of the isolated nucleons.

Nuclear engineering

The profession that deals with nuclear power.

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.

Nuclear physics

The science that describes the components of atoms.

Nuclear potential energy

The energy that is given up in decay of an unstable nucleus.

Nuclear power

The use of energy derived from nuclear chain reactions for electricity production or ship propulsion.

O

Ohm

The SI unit of electrical resistance.

Ohm's law

A law describing the relationship between resistance, current, and voltage.

Optics

The study of light.

Organic chemistry

The study of carbon compounds.

Osmosis

The spontaneous movement of molecules or ions through a semi-permable membrane, tending to equalize concentration on both sides.

P

Parallel circuit

A circuit that begins and ends at the same node as another circuit.

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.^[411] 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.

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):

[math]\displaystyle{ \mathbf{P}: \begin{pmatrix}x\\y\\z\end{pmatrix} \mapsto \begin{pmatrix}-x\\-y\\-z\end{pmatrix}. }[/math]

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.

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.^[412] Paramagnetic materials include most chemical elements and some compounds;^[413] 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.

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.^[414]

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.^[415] 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.^[416]

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.^[417][418]

Pascal's law

Pascal's law (also Pascal's principle^{[419][420][421]} 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.^[422] The law was established by French mathematician Blaise Pascal^[30] in 1647–48.^[423]

Pendulum

Is a weight suspended from a pivot so that it can swing freely.^[424] 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.

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.^[425] 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.

pH

A logarithmic measure of the concentration of hydrogen ions in an acid or base solution.

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.^{[426][427]:86[428]:3} 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 state of matter § Glass)

Phase (waves)

In physics and mathematics, the phase of a periodic function [math]\displaystyle{ F }[/math] of some real variable [math]\displaystyle{ t }[/math] (such as time) is an angle-like quantity representing the fraction of the cycle covered up to [math]\displaystyle{ t }[/math]. It is denoted [math]\displaystyle{ \phi(t) }[/math] and expressed in such a scale that it varies by one full turn as the variable [math]\displaystyle{ t }[/math] goes through each period (and [math]\displaystyle{ F(t) }[/math] goes through each complete cycle). It may be measured in any angular unit such as degrees or radians, thus increasing by 360° or [math]\displaystyle{ 2\pi }[/math] as the variable [math]\displaystyle{ t }[/math] completes a full period.^[429]

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.

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^[430][102]

[math]\displaystyle{ F = C - P + 2. }[/math]

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.^[431] The rule assumes the components do not react with each other.

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, 299792458 m/s (or about 186,282 mi/s). The photon belongs to the class of bosons.

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.

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.

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.^[433] Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.^{[lower-alpha 5][434][435][436]}

Planck constant

The Planck constant, or Planck's constant, is a fundamental physical constant denoted [math]\displaystyle{ h }[/math], 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.^[437] The SI units are defined in such a way that, when the Planck constant is expressed in SI units, it has the exact value [math]\displaystyle{ h }[/math] = 6.62607015×10⁻³⁴ J⋅s.^[438][439]

Plasma

Is one of the four fundamental states of matter, first systematically studied by Irving Langmuir in the 1920s.^[440][441] 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.

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.^[442][443] 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.

Pneumatics

The control of mechanical force and movement, generated by the application of compressed gas.

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.

Polyphase system

An electrical system that uses a set of alternating currents at different phases.

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.^[444]

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.^{[445][446][447]} Power is a scalar quantity.

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.

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.^:445[448] 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.

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][449][450]} 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%).

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.^[451][452] 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.^[453]

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.^[454] 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.^[455]

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.

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.^[456] 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

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.

Quantum field theory

In theoretical physics, quantum field theory (QFT) is a theoretical framework that combines classical field theory, special relativity and quantum mechanics,^[457]:xi 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.

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.^[458]:1.1 It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.

R

Regelation

The phenomena of melting under pressure, then freezing when the pressure is reduced.

Relative density

Relative density, or specific gravity,^[459][460] 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 4 °C or 39.2 °F); for gases, the reference is air at room temperature (20 °C or 68 °F). The term "relative density" is often preferred in scientific usage.

Relative velocity

The relative velocity [math]\displaystyle{ \vec{v}_{B\mid A} }[/math] (also [math]\displaystyle{ \vec{v}_{BA} }[/math] or [math]\displaystyle{ \vec{v}_{B \operatorname{rel} A} }[/math]) is the velocity of an object or observer B in the rest frame of another object or observer A.

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.^[461] 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.

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).^{[462][463][464]} 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.

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.

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.

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.^[465]

Rigid body

In physics, a rigid body (also known as a rigid object ^[466]) 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).

Robonaut

A development project conducted by NASA to create humanoid robots capable of using space tools and working in similar environments to suited astronauts.

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.

Robotics

Is an interdisciplinary field that integrates computer science and engineering.^[467] 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.

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).^[468] The RMS is also known as the quadratic mean^[469][470] 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.^[468] 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.

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:

[math]\displaystyle{ v_\text{RMS} = \sqrt{3RT \over M} }[/math]

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.

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:

[math]\displaystyle{ E_\mathrm{rotational} = \frac{1}{2} I \omega^2 }[/math]

where

[math]\displaystyle{ \omega \ }[/math] is the angular velocity

[math]\displaystyle{ I \ }[/math] is the moment of inertia around the axis of rotation

[math]\displaystyle{ E \ }[/math] is the kinetic energy

S

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.^[473]

Safety data sheet

A safety data sheet (SDS),^[474] 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.

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.

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')^[475]

Scalar (mathematics)

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Scalar

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Scalar multiplication

In mathematics, scalar multiplication is one of the basic operations defining a vector space in linear algebra^{[476][477][478]} (or more generally, a module in abstract algebra^[479][480]). 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).

Screw

A screw is a mechanism that converts rotational motion to linear motion, and a torque (rotational force) to a linear force.^[481] 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.^[482][483] 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.^[484][485] Geometrically, a screw can be viewed as a narrow inclined plane wrapped around a cylinder.^[481]

Series circuit

An electrical circuit in which the same current passes through each component, with only one path.

Servo

A motor that moves to and maintains a set position under command, rather than continuously moving.

Servomechanism

An automatic device that uses error-sensing negative feedback to correct the performance of a mechanism.

Shadow matter

In physics, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.^[486]

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);^[487]
• the flow induced by a force (in a fluid).

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.

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.

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.^[488] Shortwave radiation is distinguished from longwave radiation. Downward shortwave radiation is sensitive to solar zenith angle, cloud cover.^[489]

SI units

The International System of Units (SI, abbreviated from the French Système international (d'unités)) 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.

Signal processing

Is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as sound, images, and scientific measurements.^[490] 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.^[491]

Simple machine

Is a mechanical device that changes the direction or magnitude of a force.^[492] In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force.^[493] Usually the term refers to the six classical simple machines that were defined by Renaissance scientists:^{[494][495][496]}

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

Siphon

A closed tube that conveys liquids between two levels without pumping.

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.

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.

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).

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.

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.

Sound

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.

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:^{[497][498][499]}

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.

Specific heat

The amount of energy required to change the temperature of a unit mass of substance by one degree.

Specific gravity

The ratio between the mass density of a substance to that of water.

Specific volume

The volume of a unit mass of a substance.

Specific weight

The weight of a substance per unit volume.

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.^[500]

Stagnation pressure

In fluid dynamics, stagnation pressure (or pitot pressure) is the static pressure at a stagnation point in a fluid flow.^[501] 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.^[502]

Standard electrode potential

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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.

Statics

The study of forces in a non-moving, rigid body.

Statistics

Is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data.^{[503][504][505]} 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.^[506]

Steam table

Thermodynamic data table containing steam or water properties .^[507]

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 [math]\displaystyle{ j^{\star} }[/math] (also known as the black-body radiant emittance) is directly proportional to the fourth power of the black body's thermodynamic temperature T:

[math]\displaystyle{ j^{\star} = \sigma T^{4}. }[/math]

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

[math]\displaystyle{ \sigma=\frac{2\pi^5 k^4}{15c^2h^3} = 5.670374\ldots\times 10^{-8}\, \mathrm{W\, m^{-2}\,K^{-4}}, }[/math]

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

[math]\displaystyle{ L = \frac{j^{\star}}\pi = \frac\sigma\pi T^{4}. }[/math]

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, [math]\displaystyle{ \varepsilon \lt 1 }[/math]:

[math]\displaystyle{ j^{\star} = \varepsilon\sigma T^{4}. }[/math]

The radiant emittance [math]\displaystyle{ j^{\star} }[/math] 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. [math]\displaystyle{ \varepsilon }[/math] is the emissivity of the grey body; if it is a perfect blackbody, [math]\displaystyle{ \varepsilon=1 }[/math]. In the still more general (and realistic) case, the emissivity depends on the wavelength, [math]\displaystyle{ \varepsilon=\varepsilon(\lambda) }[/math]. To find the total power radiated from an object, multiply by its surface area, [math]\displaystyle{ A }[/math]:

[math]\displaystyle{ P= A j^{\star} = A \varepsilon\sigma T^{4}. }[/math]

Wavelength- and subwavelength-scale particles,^[508] metamaterials,^[509] and other nanostructures are not subject to ray-optical limits and may be designed to exceed the Stefan–Boltzmann law.

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).

Stiffness

Is the extent to which an object resists deformation in response to an applied force.^[510] The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is.^[511]

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.

Strain

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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.^[512] Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion.^[513] 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,^[514] however others can be strengthened only via work hardening, such as pure copper and aluminum.^[515]

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.

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).

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).

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.

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.^[516]

Structural load

A structural load or structural action is a force, deformation, or acceleration applied to structural elements.^[517][518] 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.^[519] Engineers often evaluate structural loads based upon published regulations, contracts, or specifications. Accepted technical standards are used for acceptance testing and inspection.

Sublimation

Is the transition of a substance directly from the solid to the gas state,^[520] without passing through the liquid state.^[521] 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.^[522] 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).^[523] 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.

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.^{[524][525][526]} Subsumption has been widely influential in autonomous robotics and elsewhere in real-time AI.

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.

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.^{[527][528][529][530]}

Superhard material

Is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test.^{[531][532][533][534]} 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.

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.