A simple experiment showing thermal expansion of air involves a balloon, a bottle and a tub of hot water. Weigh the bottle down with some pebbles and place a balloon over its top. Place the bottle in the hot water. The balloon expands within a few minutes, showing that air molecules inside the bottle are expanding.
Cool a coin and the base of a bottle in cold water; the coin must be larger than the bottle's opening. Place the coin on top of the bottle; grasp the bottle with both hands. Your body heat warms the air inside the bottle, and the air expands and moves upward. This causes the coin to "jump."
Inflate a balloon and tie off the end. Hold the balloon above a candle -- far enough away that it does not melt or catch on fire. The candle's flame warms the air molecules in the balloon -- causing them to expand -- and the balloon explodes.
This experiment requires a rubber band, a piece of cardboard cut into an arrow shape, a pin and a block of wood. Stretch the rubber band around the wooden block. Mount the cardboard arrow on the pin. Place the arrow and the pin under the rubber band. Heat the rubber band with a lit match and the arrow moves in a counterclockwise direction. The heat causes the rubber band to contract and move the arrow. Rubber contracts when heated and expands when cooled.