Specific weight
The specific weight (also known as the unit weight) is the weight per unit volume of a material. The symbol of specific weight is γ (the Greek letter Gamma).
A commonly used value is the specific weight of water on Earth at 5°C which is 9.807 kN/m3 or 62.43 lbf/ft3.
The terms specific gravity, and less often specific weight, are also used for relative density.
where
Unlike density, specific weight is not . It depends upon the value of the gravitational acceleration, which varies with location. A significant influence upon the value of specific gravity is the temperature of the material. 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.
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 lb/ft3). Specific weight can be used as a characteristic property of a fluid.
Specific weight is often used as a property of soil to solve earthwork problems.
In soil mechanics, specific weight may refer to:
where
The formula for dry unit weight is:
where
The formula for saturated unit weight is:
where
The formula for submerged unit weight is:
where
Specific weight can be used in mechanical engineering to determine the weight of a structure designed to carry certain loads while remaining intact and remaining within limits regarding deformation.
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