Convection: Movement in Fluids

In the form of heat transfer called convection, heat is transferred by the movement of molecules in a fluid from a warm region to a cooler one. The fluid may be a liquid such as water, or it may be the air or other gases. Convection is a process that combines conduction and mixing: energetic molecules move from one point in space to another, and then collide with slower particles. Convection is an influential phenomenon, contributing as it does to winds, storms, ocean currents, the heating of our homes, and the boiling of water on the stove. It occurs because air and water take up more space—become less dense—when their molecules absorb energy and move faster, and so they rise when they heat up and sink again as they cool off.