Swirling Milk

Swirling Milk

Aim

To find out what would happen to food colouring in milk once dishwashing liquid was added.

Hypothesis

I think that when the food colouring is added to the milk it will change colour. Then when the dishwashing liquid is added it will take the colour away. Just like when I wash up.

Equipment

• dishwashing liquid
• food colouring - 3 colours
• milk - blue top - room temperature
• saucer

Method

1. Pour milk into the saucer to a depth of about 4 mm.
2. Put 1 or 2 drops of the first food colour in, near the edge of the saucer.
3. Put 1 or 2 drops of the other food colours into the milk spread out around the edge of the saucer.
4. Put 2 or 3 drops of dishwashing liquid into the middle of the milk in the saucer.
5. Watch

Observations

When the food colouring was put into the milk it stayed together in a blob. When the dishwashing liquid was put into the milk the colour began to spread apart. The colours started to swirl around and when they met they merged together to form different colour combinations.

Conclusion

The food colouring stayed together, it didn’t change the colour of the milk. The dishwashing liquid did not take the colour away, it made the colour swirl around and mix faster.

Whats going on here?

The dishwashing liquid breaks down the surface tension of the fat in the milk. The dishwashing liquid sinks because it is denser than the milk. This makes the milk and the colour swirl and the dishwashing liquid sinks and the fat breaks up. As the food colouring mixes with the milk, its motion produces the beautiful patterns of swirling colour that you observe.