What To Do
For this fun kitchen experiment you may be able to get all you need by raiding the kitchen cupboards. You will need a shallow plate, milk (semi skimmed or full fat works best), food colouring, washing up liquid and a cotton bud.
Pour enough milk into the plate to cover the base. Take the food colouring and place a few drops of each colour close to the centre of the plate, some of them may start to spread out a little already but do not worry about this. Dip the cotton bud into the washing up liquid and touch it gently in the centre of the plate of milk. Watch as the food colouring starts to magically swirl around the plate in a wonderful moving piece of art.
Milk is mostly water but also contains fats that do not dissolve in water. Washing up liquid also contains molecules which are unable to dissolve in water so when you add it to the milk, the soapy molecules rush around trying to connect to the fat. By adding food colouring to the milk we get to see all this movement as the molecules rush around. Eventually the milk fat molecules are all hooked up with washing up liquid molecules and the activity slows and eventually stops.