What happens to the molecules in a fluid as it cools?

When a fluid cools, the molecules within it lose kinetic energy, leading to a decrease in their movement. As a result, the intermolecular forces become more effective, causing the molecules to come closer together. This process is known as contraction.

In most fluids, particularly liquids and gases, cooling results in a reduction in volume as the molecules occupy less space when they are less energetic. This contraction is central to various phenomena, such as the way water behaves when it freezes or how hot air rises. Understanding how molecules in a fluid behave during cooling gives insight into many natural processes and engineering applications.