# Density

## Explanation

Density is an intensive property of a material or a system and is defined as the mass of a substance per volume it occupies. Denoted by the symbol $\rho$, the SI unit of density is kg/m3.

 $\rho = \frac{m}{V}$

In some cases where the weight of the system is considered, density is expressed as weight density (or specific weight). Weight density is simply the ratio between the weight of the fluid or solid to its volume. Specific weight is expressed as N/m3 in SI units. The density of solids rarely changes with varying temperature and pressure. However, for fluids, the density changes as pressure and temperature varies.