Milk is made up mostly of water. The patterns formed with the food colouring, are down to a phenomenon called Surface Tension. This occurs because of the force of attraction between the water molecules. The water molecules on the surface, do not have like molecules on all sides, and therefore have a stronger attraction with the molecules around them. This creates a ‘film’ on the surface. The molecules in the washing up liquid, usually carry a negative charge, these molecules weaken the forces between the water molecules, thus allowing the ‘film’ to be broken.
Washing-up liquid is designed to break up surface tension, in the same way that it breaks up grease and dirt on dinner plate, for example. As a result, the washing-up liquid also breaks down the surface of the milk to create a pattern.
How its made
What you will need:
- Washing up liquid
- Food colouring
- Small bowl
- Disposable pipette
How? Pour the milk into the bowl. Add a few drops of food colouring into the milk. Using the pipette, drop small amounts of washing up liquid on to the surface of the milk. Watch what happens!