Density

Density tells you how much mass is packed into each unit of volume. It explains why some things float and others sink.

Key facts

  • Density = mass ÷ volume (kg/m³ or g/cm³).
  • Water: 1 g/cm³ = 1000 kg/m³.
  • Objects less dense than a liquid float in it.
  • Irregular shapes: find the volume by displacement in a measuring cylinder.

Worked examples

Example 1

A stone of mass 135 g raises the water in a measuring cylinder from 50 cm³ to 100 cm³. Find its density.

  1. Volume: 100 − 50 = 50 cm³.
  2. 135 ÷ 50 = 2.7 g/cm³

Answer: 2.7 g/cm³

Example 2

Will a block of density 0.8 g/cm³ float in water?

  1. 0.8 is less than 1, so it floats.

Answer: Yes