Put an empty glass bottle in the freezer overnight. Take the bottle out of the freezer and quickly put a penny over the mouth of the bottle. Hold both of your hands tightly around the bottle. The penny should begin to jump up and down because the heat from your hands flows through the glass and warms up the air inside the bottle. As the air gets warmer, it expands, pushing up on the penny and making it jump.
Used with permission from Sci-Port Discovery Center, Shreveport, Louisiana.