# Measuring the density of water 2

##### Demonstration

This method uses an equal-arm balance rather than a domestic spring balance.

#### Apparatus and materials

Equal-arm balance

Perspex boxes with internal dimensions 10 cm x 10 cm x 11 cm, 2

Mass, 1 kg

#### Health & Safety and Technical notes

If the pan size is such that the 1 kg mass might fall off, place an open cardboard box below the pan to catch it.

The boxes should have horizontal marks, on one face, 10 cm above their internal bases.

#### Procedure

a Place a box on each scale pan to show that they balance.

b Add the kilogram mass to one pan and carefully pour water into the box on the other pan until the beam balances. The water will then be seen to have a depth of 10 cm, and so a volume of 1000 cubic centimetres and a mass of 1 kg.

#### Teaching notes

1 An alternative is to measure out a kilogram of water and show it has a volume of 1000 cubic centimetres (1 litre).

2 A metre cube could be used to help students see that the mass of a cubic metre of water would be 1000 times greater.

This experiment was safety-checked in July 2006