Heat is in constant motion. It flows from warmer areas to colder areas until an overall equal temperature is established. Heat moves from one place to another in three ways: Conductions, Convection and Radiation.
Conduction
is the movement of heat through a substance (or between substances) in
contact with each other. In such cases, heat moves directly from one molecule
to another molecule in contact with it. Conduction is involved, for instance,
when heat travels from the burner to a metal pan on the stove. In a home, insulation
is used to minimize heat movement by conduction.
Convection
is the movement of heat by the actual movement of a heated gas or liquid.
For example, warm air (or water) is less dense than cooler air (or water) and
therefore rises, while cold, more dense, air (or water) falls. This is the mechanism
for lifting hot air balloons. As air is heated, it becomes less dense and rises
into the balloon. Because air contained in the balloon is less dense than the
surrounding air, it rises off the ground. In homes, a special case of convection
known as "infiltration" occurs when air moves into and out of the
home through cracks and other openings in the envelope.
Radiation
is the movement of heat away from an object by means of "electromagnetic
waves" or "infrared" rays. This process involves only the molecules
of the substance radiating the heat. Radiation can occur through a vacuum and
is the mechanism by which the heat of the sun is transferred to earth. If you
sit in front of a hot stove or fire you will feel the "radiated" heat.
