Purpose
In this activity, you will investigate the difference between hot water and cold water—on the molecular level.

Discussion
The difference between hot things and cold things is referred to as temperature. The temperature of an object depends on the kinetic energy of the random motions of its molecules. A thermometer can be used to measure temperature, but we can't always tell a hot thing from a cold thing just by looking at it. Consider a glass of hot water and a glass of cold water side by side. The water molecules in each glass don't appear to be moving differently from each other. But they are. Follow the steps below to see the difference.