Density

Key Stage 3

Density is the amount of mass per unit volume of an object.

An object with a large amount of mass in a small volume is said to have a high density.

An object with a small amount of mass spread over a large volume is said to have a low density.

The units of density are kg/m³.


Solids are the most dense state of matter because there are a large number of particles in a certain volume and gases are the least dense state of matter because there are a small number of particles in a the same volume.

If an object is more dense than water it will sink.

If an object is less dense than water it will rise through water and float on the surface.

Density = Mass/volume

\[\rho = \tfrac{m}{V}\] Where:

5000kg of Iron has a volume of 0.635m³. Calculate the density of Iron.	A 50,000cm³ container of water is full with a 50kg mass of water. Calculate the density of water.	A 200,000cm³ volume of air has a mass of 245g. Calculate the density of air.
Mass = 5000kg Volume = 0.635m³ \[\rho = \tfrac{m}{V}\] \[\rho = \tfrac{5000}{0.635}\] \[\rho = 7874kg/m<sup>3</sup>\]	Mass = 50kg Volume = 50,000cm³ = 0.05m³ \[\rho = \tfrac{m}{V}\] \[\rho = \tfrac{50}{0.05}\] \[\rho = 1000kg/m<sup>3</sup>\]	Mass = 245g = 0.245kg Volume = 200,000cm³ = 0.2m³ \[\rho = \tfrac{m}{V}\] \[\rho = \tfrac{0.245}{0.2}\] \[\rho = 1.225kg/m<sup>3</sup>\]