What Is Heat?
 

Heat is a special kind of energy transfer that can take place from one material object, place, or region to another. For example, if you place a kettle of water on a hot stove, heat is transferred from the burner to the water. This is conductive heat, also called conduction (Fig. 1a). When an infrared lamp, sometimes called a heat lamp, shines on your sore shoulder, energy is transferred to your skin surface from the filament of the lamp; this is radiative heat, also called radiation (see Fig. 1b). When a blowertype electric heater warms up a room, air passes through the heating elements and is blown by a fan into the room, where the heated air rises and mixes with the rest of the air in the room. This is convective heat, also called convection (see Fig. 1c).
Copyright 2002 by The McGraw-Hill Companies, Inc. Click here for Terms of Use.

Fig. 1. Examples of energy transfer, in the form of heat, by conduction (a), radiation (b), and convection (c).

Heat is not quite the same thing as energy, although the units of heat and energy are defined in the same physical dimensions. Heat is the transfer of energy that occurs when conduction, radiation, and/or convection take place. Sometimes the energy transfer takes place in only one of these three modes, but sometimes it occurs in two or all three.