Sink or swim
What you'll need:
* corn syrup
* green and blue food coloring
* vegetable oil
* a paper clip
* a grape
* a plastic bottle top
* Pour one inch of corn syrup into a tall glass or jar and stir in a drop of green food coloring.
* Have your child mix a drop of blue food coloring into a cup of water. Let him carefully pour the water on top of the syrup.
* Add one inch of vegetable oil on top of the water.
* Once the liquids have formed distinct layers, have him drop into the jar a paper clip, then a grape, then a small plastic bottle top.
* Watch how the objects slowly fall and eventually settle on different layers.
How it works: Corn syrup, water, and oil are all made up of tiny particles called molecules. The more tightly packed the molecules, the more dense --or heavy --the liquid. Here, the syrup is the heaviest liquid, followed by the water, and then the vegetable oil, which explains why the syrup sits on the bottom of the jar, the water is in the middle, and the oil rests on top. The same holds true for the objects dropped into the jar: The paper clip is most dense, so it falls to the bottom. A grape is less dense, so it sits in the middle of the jar, at the bottom of the water. The bottle top is the least heavy, so it floats on top, in the oil.