Most matter expands when heated and contracts when cooled, a principle called thermal expansion. The average kinetic energy of the particles increases when matter is heated and this increase in motion increases the average distance between its atoms.

What happens to matter when it is cooled?

When a substance is heated, it gains thermal energy. Therefore, its particles move faster and its temperature rises. When a substance is cooled, it loses thermal energy, which causes its particles to move more slowly and its temperature to drop.

Why does matter contract when cooled?

Explanation: As the molecules of a liquid are cooled they slow down. As the molecules slow down they take up less volume. Taking up less room because of the molecules lower energy causes the liquid to contract.