For this experiment, you will need two bottles of warm water and two bottles of cold water. Use food coloring to dye the cold water one color and the warm water another so that you can see the difference between the two. Place an index card over the mouth of a bottle of cold water. Turn the bottle upside down over a bottle of warm water and remove the index card. The cold water from the top bottle should begin to move into the bottom bottle of warm water. Now, reverse the experiment with the other two bottles, placing the warm water on top and the cold water on the bottom. When you remove the index card, the water should remain separate, demonstrating that cold water is heavier than warm water.
Water is a poor conductor of heat because it absorbs it quickly. This can be demonstrated by placing an ice cube at the bottom of a test tube or jar filled with room temperature water. Once the cube has sunk to the bottom, place a flame over the top of the test tube or jar. This will make the water at the top boil, but the ice cube will remain intact because the heat will not reach the bottom of the jar or tube.
For this experiment you will need a screw and its matching nut. Test the fit by placing the screw in the nut before the experiment. You should be able to screw them together easily. Heat the screw over a Bunsen burner for several minutes. Remove it from the heat before the head of the screw becomes too hot to touch. When you try to place the screw in the nut it will be too big, demonstrating how metals expand when heated.
Fill a clear jar with water. Tear a piece of paper into very small pieces and drop these into the jar. Let them settle to the bottom and then place the jar over a Bunsen burner. As the currents of heat move through the water, you will be able to see them by the way they move the paper particles. The particles will move along the lines of heat. This is a great way to demonstrate the movement of heat through liquid.