Here's why:

* Temperature is a measure of average kinetic energy. Kinetic energy is the energy of motion.

* Higher temperature means higher average kinetic energy. So, molecules are moving faster on average.

* Think of it like this: Imagine a pot of water on the stove. As you heat it, the molecules inside move faster and faster, eventually boiling and turning into steam.

This relationship is described by the kinetic theory of gases, which states that the average kinetic energy of gas molecules is directly proportional to the absolute temperature.