In the other put cold water with a different coloring. Pour the warm water slowly into a container already half-full with the cold water. If done correctly you should be able to see the warm water float on top of the cold water. Click here to see setup diagram. Students should be able to tell not only which substance went to which level but also why.
Density determines the relative bouyancy of objects or fluids.
Out of the oil, water, and corn syrup, oil is the least dense so it floats on the water. The corn syrup is more dense so the water floats on top of it. Warm water is less dense than cold water - as the temperature increases, the motion of the tiny water molecules increases and they spread out more, which renders the liquid less dense as a whole. On the other hand, cold water is more dense because the cold water molecules move more slowly and are much closer together. Winds blow the surface water.