d=m/v

where d=density, m=mass and v=volume.

The object can be anything small enough to fit into a measuring cylinder such as a small stone, blob of plasticine, lego brick etc.

Firstly the student can find the mass of the object by placing it on a pan-top balance or by using a spring balance (see Fig 1) Then the object is placed into a measuring cylinder half filled with water (see Fig 2). The water it displaces is equal to its mass. A eureka can can be used instead of a measuring cylinder for this practical.

To find the density of the object, the mass is simply divided by the volume. The result is measured in kg/m³.

Equipment required (per set):

• An object (stone, plasticine etc)
• Measuring cylinder or density (eureka) can
• Pan-top balance or spring balance

Geologists sometimes use this method to find the density of rocks. This helps them identify its type.