### KS3 Physics

Energy
Motion and Forces
Waves
Electricity and Electromagnetism
Matter
Space Physics

# Density

When looking at density, it is important to first understand states of matter. The three common states of matter are solidsliquids and gases.

Let’s look at the arrangement of particles in these three states.

## Arrangement of Particles

### Solids

The image below shows the arrangement of particles in a solid.

The particles are very close together in a regular lattice shape. Solids keep a fixed shape, meaning the particles are unable to move around.

However, the particles are able to vibrate under certain conditions. For example, when heated, the particles begin to vibrate in their fixed positions.

### Liquids

The image below shows the arrangement of particles in a liquid.

Liquid particles are arranged in random positions. This is because the forces between them are weak. However, some of the particles are still close together.

Liquids take the shape of containers because they can flow.

The liquid particles are always moving randomly. Similar to solids, when heated, the particles vibrate more.

### Gases

The image below shows the arrangement of particles in a gas.

Gas particles have very weak forces between them, so they are able to move around freely. As you can see, the particles are very far apart from each other.

Gases can always take the shape of containers because they have no definite shape.

When you increase the level of heat, gas particles move faster.

## Understanding Density

The density of an object is its mass for a given volume. For example, let’s compare two blocks with the same volume.

• The high-density block has a lot of mass packed into its volume
• The low-density block has a lower mass packed into the same volume

## Calculating Density

To calculate the density of an object, we need:

• The mass of the object
• The volume of the object

The mass of the object can be measured using a balance and a measuring cylinder can be used to measure the volume of a liquid. To measure the volume of a solid, measure its side.

The equation to calculate density is:

• ρ = Density in grams per centimetre cubed (g/cm3)
• M = Mass in grams (g)
• V = Volume in centimetres cubed (cm3)

## Example

A rock has a mass of 15 kg and a volume of 1 m3. Calculate the density.

Looking back at the equation:

Density (g/cm3) = Mass (g) ÷ Volume (cm3)

We know 15 kg = 15000 g and 1 m3 = 100 cm3

So Density = 15000 g ÷ 100 cm3 = 150 g/cm3

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