Storm in a Saucer

Science concepts

Milk is a mixture of oil and water (emulsion).
Detergent mixes with both oil and water.

Special instructions

While starting out separately the colours quickly swirl together when detergent is added.

Teachers should conduct their own risk assessment of this activity.

Class time required: 15 minutes

Materials

• A saucer or small plastic plate
• Full cream milk
• Skim milk
• Food colouring (three colours)
• Detergent in a small cup
• Match stick

What to do

1. Pour some full cream milk into the plate.
2. Carefully place one drop of each type of food colouring into the milk, making sure the drops are in different areas of the plate.
3. Dip the matchstick into the detergent and use it to place a drop of detergent next to each drop of food colouring.

What happens when you add the detergent?

Can you think why this happens?

Repeat the experiment using skim milk – is there any difference?

What’s happening?

Milk is an emulsion. It is a stable mixture of mostly fat and water which do not normally mix together.
When you add detergent to milk, the fat and water are attracted to it and swirl around in a disorderly motion.

The food colouring helps you see this movement.

Full cream milk swirls the food colouring more dramatically because it has a higher fat content than skim milk.