Changes of specifi
Changes of specific weight
Unlike density, specific weight is not absolute. 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. [2]
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Uses
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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., lb/ft3 or N/m3). Specific weight can be used as a characteristic property of a fluid. [2]
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Soil mechanics
Specific weight is used as a property of soil often used to solve earthwork problems.
In soil mechanics, specific weight may refer to:
- Moist unit weight, which is the unit weight of a soil when void spaces of the soil contain both water and air.
where
-
is the moist unit weight of the material
-
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, which is 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:
where
-
is the moist unit weight of the material
-
is the dry unit weight of the material
-
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, which is 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:
where
-
is the saturated unit weight of the material
-
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[3]
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Mechanical engineering
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.