Convection refers to transfer of heat by a fluid material (such as air or water) moving from one place to another. The convection is forced if the fluid motion is caused by a fan or a pump while natural convection is the result of density differences.

A simple fan presents a question: why do we feel cooler if cool air is moving across our skin, even though the air itself is the same temperature as the still air? The answer lies in the fact that the layer of air next to our skin forms a thin blanket of still air that conducts heat slowly. If the still air is stripped away by wind, the “blanket” is removed and the skin is directly exposed to the air temperature. This model compares moving air and still air around a hot object.