Density (CIE A Level Physics)

• Density is the mass per unit volume of an object

• Where:
  • ρ (the Greek letter rho) = density in kilograms per metre cubed (kg m^-3)
  • m = mass in kilograms (kg)
  • V = volume in metres cubed (m³)
    

• Gases are less dense than liquids, which are less dense than solids
• This is because there are fewer particles, and therefore less mass, per unit volume

Relative density of a gas and a solid

Gases are less dense than solids because they have fewer particles, and therefore less mass, per unit volume

• The volume of an object may not always be given directly, but can be calculated with the appropriate equation depending on the object’s shape

Calculating the volumes of different shapes

Expressions for calculating the volume of a sphere, a cube and a cylinder