When particles in a liquid are cooled, their average kinetic energy decreases. This means that the particles move more slowly and have less energy to overcome the forces of attraction between them. As a result, the particles become closer together and the liquid becomes denser. In some cases, the particles may even become so close together that they form a solid.

The process of cooling a liquid to form a solid is called freezing. Freezing is an important process in nature and has many applications in industry and everyday life. For example, freezing is used to preserve food, make ice, and cool computer systems.