Storm in a Saucer

Have you ever wanted to control the weather? Well now you can create your very own storm in a saucer!

Australian Curriculum links

  • Science > Chemical Sciences > Year 2 > ACSSU031
  • Science > Chemical Sciences > Year 6 > ACSSU095

You'll need

  • saucer or small plastic plate
  • full cream milk
  • food colouring (three colours)
  • detergent in a small cup
  • toothpick

Try this

  1. Pour some full cream milk into the dip of the saucer.
  2. Carefully place one drop of each type of food colouring into the milk, making sure the drops are in different locations.
  3. Dip the toothpick into the detergent and use the toothpick to place a drop of detergent next to each drop of food colouring.
  4. Observe what happens.

Further investigation

Repeat the experiment using skim milk. Why do you think the results were different?

What's happening?

Milk is made up of mostly water and small amounts of proteins and fat globules. Water usually doesn't mix with oil or fats, however, proteins in the milk help blend the water and fat together in a stable solution known as an 'emulsion'. Adding a drop of detergent breaks the chemical bonds in the emulsion causing the fats and proteins to move around. This movement helps make little currents in the milk, which we can see using the food dye.

Like proteins, detergents can also help fats and water mix together. They do this by forming little pockets of detergent called 'micelles' that the fat globules can sit inside. Adding the detergent to the milk makes micelles form around the fat globules, which changes the size and number of fat globules within the milk. As the fats and detergent rush around the milk to try and set up this new arrangement, the food dye is pushed around and makes the swirling patterns.

But why does the big swirling pattern spread out from the middle of the detergent drop? It's because the detergent breaks the surface tension of the milk. Surface tension is like a very thin skin that forms on the top of all liquids. Milk has a very high surface tension because little bits of milk called 'molecules' hold onto each other very tightly. But, as soon as detergent enters the milk, the detergent molecules settle on the surface, pushing apart the milk molecules. This reduces the surface tension at that point, and causes a wave of milk to rush to the edge of the saucer. You can imagine the milk on the surface like a tightly stretched piece of balloon rubber. If you poke a hole in the middle, the rubber will quickly be pulled away from the centre as the rubber around it snaps back. In the milk, it is this fast wave which starts the milk moving in the swirling pattern we see.

Further information

Mayonnaise is an emulsion that has been around for 254 years! Most food historians believe it was invented by the French and purely by accident. Apparently after the Duke of Richelieu captured the Spanish city of Mahon, a victory feast was planned in his honour. His head chef was advised to make a sauce of cream and eggs but he realised there was no cream left in the kitchen. As it was the year 1756 and he couldn't just nip down to the local supermarket, he had to think very quickly on his feet. He used olive oil instead of cream and voila, a new food sensation was born. The special sauce was named "Mahonnaise" in honour of the Duke's victory over the town of Mahon.