The transfer of heat energy produced by natural movements of liquids or gases. When heat is applied to a liquid or gas, its mass is reduced, so it has a tendency to rise upward. Thus the currents created by convection usually travel in an upward direction. Convection is a cyclical process, so while warmer currents are travelling upward, other cooler currents must travel downward somewhere else. The downward travel of cooler currents isn't usually as noticeable, and typically happens over a much wider area.

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