To demonstrate how warm water will rise and cold water will sink
- Two plastic water bottles (20 oz. approximately)
- Hot and cold water
- Food coloring (any dark color)
- Index card
- Plastic mixing bowl
Fill one bottle to the top with cold water. Put a few drops of food coloring in the other bottle and add hot water. Let the water be as hot as it can be without burning you or melting the plastic bottle. Stand the hot water bottle in the plastic bowl. Place the index card over the mouth of the cold-water bottle. Flip it over carefully. Put the cold-water bottle over the hot water bottle so the mouths are lined up. Slide the card out. See what happens.
The colored water rises from the bottom bottle into the top bottle. Cold water is denser and sinks. The cold water pushes the hot water beneath it upward. This process happens with air as well. It is called convection. It affects how heat is moved around the Earth.