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The density of a substance is the mass per unit volume. In other words, it tells you how much (volume) of something will weigh (mass). The density of a substance is found by ## Units

The standard units of density (SI) is the kilogram per cubic metre (kg/m3). Other density units for GCSE are the gram per cubic centimetre (g/cm3). To convert from g/cm3 to kg/m3, you multiply by 1000 or 103.

## Working out the mass

Use a balance. With a gas or liquid, measure the beaker or flask with either just air in (liquid), or with a vacuum in (gas). Then measure mass with gas or liquid in the beaker/flask. Take the second reading from the first to find the mass.

## Working out the volume

### Regular solids

Measure the dimensions and thus work out the volume.

### Irregular solids

Use a displacement can: Fill it up so it over-flows, when all the water possible has drained out, put the solid in the displacement can, and measure the volume of the water that comes out of the can using a measuring cyclinder.

### Liquids or gases

Use a flask or a measuring cylider.

## Floating or sinking

If an object has a higher density than the fluid it is in, it sinks. If it has a lower density, it floats. For example, glass (d = 2.5g/cm3) sinks in water (d = 1g/cm3), but floats in mercury (d = 13.6g/cm3)

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