Specific weight

Short description: Weight per unit volume of a material

Not to be confused with Specific gravity, Specific density, or Specific force.

The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight W divided by the volume V of a material: γ=W/V. Equivalently, it may also be formulated as the product of density, ρ, and gravity acceleration, g: γ=ρg. Its unit of measurement in the International System of Units (SI) is the newton per cubic metre (N/m3), expressed in terms of base units as kg⋅m−2⋅s−2. A commonly used value is the specific weight of water on Earth at 4 °C (39 °F), which is 9.807 kilonewtons per cubic metre or 62.43 pounds-force per cubic foot.[1]

## Contents

* 1 Discussion
* 2 Applications
* 2.1 Fluid mechanics
* 2.2 Soil mechanics
* 2.3 Civil and mechanical engineering
* 3 Specific weight of water
* 4 Specific weight of air
* 5 References
* 6 External links

## Discussion

The density of a material is defined as mass divided by volume, typically expressed with the unit kg/m3. Unlike density, specific weight is not a fixed property of a material, as it depends on the value of the gravitational acceleration, which varies with location (e.g., Earth's gravity). In practice, the standard gravity (a constant) is often assumed, usually taken as 9.80665 m/s2.

Pressure may also affect values, depending upon the bulk modulus of the material, but generally, at moderate pressures, has a less significant effect than the other factors.[2]

## Applications

### Fluid mechanics

In fluid mechanics, specific weight represents the force exerted by gravity on a unit volume of a fluid. For this reason, units are expressed as force per unit volume (e.g., N/m3 or lbf/ft3). Specific weight can be used as a characteristic property of a fluid.[2]

### Soil mechanics

Specific weight is often used as a property of soil to solve earthwork problems.

In soil mechanics, specific weight may refer to:

Moist unit weight
The unit weight of a soil when void spaces of the soil contain both water and air. γ=(1+w)Gsγw1+e where

* γ is the moist unit weight of the material
* γw is the unit weight of water
* w is the moisture content of the material
* Gs is the specific gravity of the solid
* e is the void ratio

Dry unit weight
The unit weight of a soil when all void spaces of the soil are completely filled with air, with no water. The formula for dry unit weight is: γd=Gsγw1+e=γ1+w where

* γ is the moist unit weight of the material
* γd is the dry unit weight of the material
* γw is the unit weight of water
* w is the moisture content of the material
* Gs is the specific gravity of the solid
* e is the void ratio

Saturated unit weight
The unit weight of a soil when all void spaces of the soil are completely filled with water, with no air. The formula for saturated unit weight is: γs=(Gs+e)γw1+e where

* γs is the saturated unit weight of the material
* γw is the unit weight of water
* Gs is the specific gravity of the solid
* e is the void ratio[3]

Submerged unit weight
The difference between the saturated unit weight and the unit weight of water.[4] It is often used in the calculation of the effective stress in a soil. The formula for submerged unit weight is: γ′=γs−γw where

* γ′ is the submerged unit weight of the material
* γs is the saturated unit weight of the material
* γw is the unit weight of water

### Civil and mechanical engineering

Specific weight can be used in civil engineering and mechanical engineering to determine the weight of a structure designed to carry certain loads while remaining intact and remaining within limits regarding deformation.

## Specific weight of water

Specific weight of water at standard sea-level atmospheric pressure (metric units)[2] Temperature (°C)  | Specific weight (kN/m3)

|

0 | 9.805
5 | 9.807
10 | 9.804
15 | 9.798
20 | 9.789
25 | 9.777
30 | 9.765
40 | 9.731
50 | 9.690
60 | 9.642
70 | 9.589
80 | 9.530
90 | 9.467
100 | 9.399
Specific weight of water at standard sea-level atmospheric pressure (imperial units)[2] Temperature (°F)  | Specific weight (lbf/ft3)

|

32 | 62.42
40 | 62.43
50 | 62.41
60 | 62.37
70 | 62.30
80 | 62.22
90 | 62.11
100 | 62.00
110 | 61.86
120 | 61.71
130 | 61.55
140 | 61.38
150 | 61.20
160 | 61.00
170 | 60.80
180 | 60.58
190 | 60.36
200 | 60.12
212 | 59.83

## Specific weight of air

Main article: Physics:Density of air

Specific weight of air at standard sea-level atmospheric pressure (metric units) [2] Temperature (°C)  | Specific weight (N/m3)

|

−40 | 14.86
−20 | 13.86
0 | 12.68
10 | 12.24
20 | 11.82
30 | 11.43
40 | 11.06
60 | 10.4
80 | 9.81
100 | 9.28
200 | 7.33
Specific weight of air at standard sea-level atmospheric pressure (imperial units) [2] Temperature (°F)  | Specific weight (lbf/ft3)

|

−40 |
−20 | 0.0903
0 | 0.08637
10 | 0.08453
20 | 0.08277
30 | 0.08108
40 | 0.07945
50 | 0.0779
60 | 0.0764
70 | 0.07495
80 | 0.07357
90 | 0.07223
100 | 0.07094
120 | 0.06849
140 | 0.0662
160 | 0.06407
180 | 0.06206
200 | 0.06018
250 | 0.05594

## References

1. ↑ National Council of Examiners for Engineering and Surveying (2005). Fundamentals of Engineering Supplied-Reference Handbook (7th ed.). ISBN 1-932613-00-5.
2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Finnemore, J. E. (2002). Fluid Mechanics with Engineering Applications. New York: McGraw-Hill. ISBN 0-07-243202-0.
3. ↑ Das, Braja M. (2007). Principles of Geotechnical Engineering. Canada: Chris Carson. ISBN 0-495-07316-4.
4. ↑ The Transtec Group, Inc. (2012). Basic Definitions and Terminology of Soils. [1] (Page viewed December 7, 2012

## External links

* Submerged weight calculator
* Specific weight calculator
* http://www.engineeringtoolbox.com/density-specific-weight-gravity-d_290.html
* http://www.themeter.net/pesi-spec_e.htm

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Specific weight. Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Physics:Specific_weight&oldid=3843959"