This is a great science experiment for very little people, since they don't need to understand any of the why but will enjoy watching it! Its also great for older kids to demonstrate an important chemical principal, that some molecules are polar (they have a negative and a positively charged end because of an imbalance of electronegativity in the molecule), and some non-polar (there is no imbalance, and so no charged ends of the molecule) - which is where soap and detergents come in!
Milk contains both water (polar) and fat (non-polar) molecules. The fat molecules aren't dissolved in the water. We use detergent to "dissolve" fats, and clean them off surfaces - which we couldn't do with just water. This is because detergents have both polar and non-polar ends to their molecules. The non-polar end can attach to the fats and the polar end can attach to the water. So the detergent works to connect the fat to the water, so it can be washed away!
In this experiment, you add a drop of detergent to some milk, and thanks to some drops of food colouring you can watch it working on the milk - spreading out and "grabbing onto" the fat and water molecules, and making swirling tumbling patterns in the water as it does so.
Or you can just enjoy the magic of watching the reaction as you do it.
To make the magic milk experiment you will need:
a shallow dish or plate
milk (full cream works best)
a cotton wool bud
dishwashing detergent (you'll need a liquid one)
Step 1: Pour some milk into the shallow dish (we used ikea plastic plates).
Step 2: Put a couple of drops of food colouring into the milk, so that they are not touching each other.
Step 3: Dip the end of your cotton wool bud into the dishwashing detergent and place the detergent end into the middle of the milk in the dish.
Step 4: Watch as the milk swirls and churns, as the detergent molecules attach themselves to both the fat and the water parts of the milk!