Weight density, also known as specific weight, is a physical property that represents the weight of a substance per unit volume. It is a measure of the force exerted by gravity on a specific volume of a material. Weight density is commonly used in the field of fluid mechanics to analyze the behavior of fluids, but it can also be applied to solids.
The weight density (γ) of a substance is calculated by dividing its weight (W) by its volume (V):
γ = W / V
The unit of weight density depends on the unit of weight and volume used in the calculation. In the International System of Units (SI), weight is typically measured in Newtons (N), and volume is measured in cubic meters (m³). Therefore, the unit of weight density in SI units is Newtons per cubic meter (N/m³). However, other units such as pounds-force per cubic foot (lb/ft³) or pounds per cubic inch (lb/in³) are also used in different systems of measurement.
Weight density is influenced by the mass of the substance and the acceleration due to gravity. It is important to note that weight density is not the same as density, which is defined as mass per unit volume and is independent of the gravitational field. Density is typically represented by the Greek letter "ρ" (rho), while weight density is represented by the Greek letter "γ" (gamma).