How Heat Travels

	Conduction is the movement of heat through a material. When heat travels by conduction, it moves through a material without carrying any of the material with it. For example, heat from a burner makes the atoms on the underside of a frying pan vibrate faster. These atoms then strike atoms above them. In this way, heat passes through the pan to the food inside it.
	Convection is the transfer of heat by the movement of a heated material. A space heater, for example, warms the air around it. This heated air rises and is replaced by cooler air. The movement of air creates a convection current that carries hot air through a room. Convection occurs in liquids as well as gases. For example, convection currents will form in a pan of cold water on a hot stove. As the water near the bottom warms up and expands, it becomes lighter than the cold water near the top of the pan. This cold water sinks and forces the heated water to the top. The convection current continues until all the water reaches the same temperature.
	Radiation carries heat in the form of waves through space. Heat causes a wire in a heat lamp to give off waves of radiant energy called infrared rays. These rays travel through space in much the same way as water waves travel on the surface of a pond. When the radiant energy strikes an object, it speeds up the atoms or molecules in that object, thereby making that object (or person) warmer. Much energy from the sun travels through space to the earth, warming the earth's surface.

Squire, Charles F. "Heat." The World Book Encyclopedia. Chicago:World Book-Childcraft International, Inc., 1979.