Explain that warm molecules move around a lot and they like to spread out away from eachother. Ask students to do this by walking, bouncing, or dancing. The hotter the molecules are, the faster they move. Ask students to act like hot molecules. Next they are going to become cold molecules.
Cold molecules like to huddle together and bounce slowly.
The colder the molecules are slower they bounce, and when they freeze they bounce really slowly, but they don't stop moving. Ask students to act like frozen molecules. Now give students cues as to how they should act like. Start off changing cues slowly but then get faster, see if the class can respond right away.