Density is an example of a **compound measure,** which is one that involves more than one unit of measurement.

Density is a measure of mass (e.g. kg, g) in relation to unit volume (e.g. m^{3}, cm^{3},) and can be measured in kg/m^{3}, g/cm^{3}, etc.

You should know the following formulae and may find the triangle helpful for remembering the three mass, density and volume formulae.

**Example 1**

A large block of oak has a mass of 185 kg and a volume of 0.25 m^{3}.

Find its density in kg/m^{3}.

**Answer**

**Density** = Mass ÷ Volume = 185 ÷ 0.25 = **740 ** kg/m^{3}.

**Example 2**

Aluminium has a density of 2.712 g/cm^{3}. Find the mass of a piece of aluminium with a volume of 12 cm^{3}.

Give your answer to 3 sig. figs.

**Answer**

Mass = Density x Volume

**Mass **= 2.712 x 12 = **32.5 g**

Now let's apply these formulae by tackling some questions together!