The specific weight, also known as the unit weight (symbol , the Greek letter gamma), is a volume-specific quantity defined as the weight divided by the volume of a material:
Equivalently, it may also be formulated as the product of density, , and gravity acceleration, :
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 , which is .National Council of Examiners for Engineering and Surveying (2005). Fundamentals of Engineering Supplied-Reference Handbook (7th ed.). .
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 .
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.
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.
Soil mechanics Specific weight is often used as a property of soil to solve earthwork problems.
In soil mechanics, specific weight may refer to:
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) 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)Finnemore, J. E. (2002). Fluid Mechanics with Engineering Applications. New York: McGraw-Hill. . 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
+ Specific weight of air at standard sea-level atmospheric pressure (metric units) 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) 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