# 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 ${\displaystyle \rho }$, the SI unit of density is kg/m3.

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

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.

### How does temperature affect density?

Heating up a system increases the energy of the system. Increasing the temperature mostly affects fluids than solids, as the molecules are free to move around in liquid and gas states. The kinetic energy of the molecules increases and they expand in volume, thus decreasing the density. When the temperature is brought down, the energy decreases and the density increases.

### How does pressure affect density?

Increase in pressure would directly decrease the volume of any given fluid or solid by compressing it. The pressure packs all the molecules closely and densely, thereby increasing the density of it. A good example of this is the water in the ocean surface and the ocean floor. At the surface the water's density is 1029 kg/m3. Due to its own pressure under gravity, the density of water at the ocean floor can reach higher than 1050 kg/m3.