MAKE A THERMOMETER
Fill about 1/4 of the bottle full with equal parts of water and rubbing alcohol.
Add a few drops of food coloring.
Put the straw in the bottle, but don't let it touch the bottom.
Use the modeling clay to seal the neck of the bottle, so the straw stays in place. (Make sure the straw does not touch the bottom of the bottle.)
Hold your hands on the bottom of the bottle and watch the mixture move up through the straw.
Why does this happen? Just like any thermometer, the mixture expanded when it was warmed. This made the mixture no longer fit in the bottom of the bottle. As the alcohol expanded the colored mixture moved up through the straw. If the bottle were to get extremely hot, the mixture would have come up through the top of the straw.