Pour a tablespoon of vegetable oil into a mug. Add two drops each of red and blue food coloring. Stir until the food coloring breaks up into tiny drops. Pour the mixture into a glass of water and watch what happens.
How It Works
This activity shows two ideas at work. The first is that water does not mix well with oil. When you stir drops of food coloring into the oil, they break up into droplets because food coloring is made up mostly of water. When you pour the mixture into the water, the oil does not dissolve into the water for the same reason.
The second idea is that water is denser than oil. (A cup of water weighs more than a cup of oil.) That's why the mixture of oil and food coloring floats on the water. The droplets of food coloring are also denser than the oil.They slowly sink to the bottom of the oil layer. As each droplet touches the water, it begins to mix into the water, flowing downward in a tiny burst of color.