Learners observe and conduct experiments demonstrating the different properties of hot and cold materials. In a demonstration, learners observe that food coloring mixes faster in hot water than in cold. In a second demonstration, learners observe that air in a bottle expands when heated. As an activity, learners examine the behavior of air inside bottles submerged in hot and cold water. Use these experiments to introduce the molecular properties of matter and the process of phase changes. The demonstrations can also be conducted as individual activities.