Measuring volume

To calculate density, the volume of the material must be known.

If the object is a regular shape, the volume can be found by measuring length, breadth and height and using the equation:

Volume = length x breadth x height

Regular shaped object with length, breadth and height labelled

If the object has an irregular shape, the volume can be measured using a measuring cylinder or a displacement can.

The volume of the stone can be found by subtracting the volume of the water without the stone from the volume of the water with the stone.

Volume of stone = Final Volume – Initial Volume

Volume of stone = 75 cm3 – 50 cm3 = 25 cm3

If the mass of the stone is measured using a top pan balance and found to be 175 g.

\rho = \frac{m}{v}

\rho = \frac{175~g}{{25~cm}^3}

Density of the stone is 7 g/cm3

The volume of larger irregular objects can be measured using a displacement can.

Displacement can used to measure the volume of an irregular shaped object.
  1. Place the stone on the top pan balance and measure its mass.
  2. Fill the displacement can until the water is level with the bottom of the pipe.
  3. Place a measuring cylinder under the pipe ready to collect the displaced water.
  4. Carefully drop the stone into the can and wait until no more water runs into the cylinder.
  5. Measure the volume of the displaced water.
  6. Use the measurements of mass and volume to calculate the density of the stone.