Density and compound measures

A compound measure combines two measurements, like speed (distance and time), density (mass and volume) and pressure (force and area). They all work with a formula triangle.

Key facts

  • Speed = distance ÷ time.
  • Density = mass ÷ volume.
  • Pressure = force ÷ area.
  • Check units match: km with hours, m with seconds, g with cm³.
  • km/h to m/s: divide by 3.6.

Worked examples

Example 1

A gold bar has mass 19.3 kg and volume 1000 cm³. Find its density in g/cm³.

  1. 19.3 kg = 19 300 g.
  2. Density = mass ÷ volume. 19300 ÷ 1000 = 19.3

Answer: 19.3 g/cm³

Example 2

Change 72 km/h into m/s.

  1. 72 km = 72 000 m; 1 hour = 3600 s.
  2. 72000 ÷ 3600 = 20

Answer: 20 m/s