Specific weight
The specific weight, also known as the unit weight (symbol γ, the Greek letter gamma), is a volume-specific quantity defined as the weight per unit volume of a material.
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.<ref name="FE">National Council of Examiners for Engineering and Surveying (2005). Fundamentals of Engineering Supplied-Reference Handbook (7th ed.). ISBN 1-932613-00-5. </ref>
Definition
The specific weight, γ, of a material is defined as the product of its density, ρ, and the standard gravity, g: <math display=block>\gamma = \rho \, g</math>
The density of the material is defined as mass per unit volume, typically measured in kg/m3. The standard gravity is acceleration due to gravity, usually given in m/s2, and on Earth usually taken as 9.81 m/s2.
Unlike density, specific weight is not a fixed property of a material. It depends on the value of the gravitational acceleration, which varies with location. 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.<ref name="fluids" />
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.<ref name="fluids" />
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
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- Dry unit weight
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- Saturated unit weight
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- Submerged unit weight
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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
| 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 |
| 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
| 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 |
| 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
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
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