This heat flow occurs when two solid bodies of differing temperatures come into physical contact, or when one solid body experiences a temperature difference from one area to another. Convection is the transfer of heat through the movement of a liquid or gas such as water or air. A good example is the uniform heating of water in a tea kettle. Water heated at the bottom of the kettle rises, allowing cooler water to move to the bottom, where it is then heated. This continuous stirring action brings the whole body of water to a near uniform temperature.
Radiation is the transfer of heat energy via the electromagnetic radiation emitted by an object.
This radiation is emitted by objects in all directions without need of a solid or fluid to transfer the heat. The heat felt around a dying campfire from the glowing embers is felt primarily as a result of thermal radiation. Electromagnetic Spectrum Human beings and most animals see only a small portion of the radiation that makes up the electromagnetic spectrum. We call this radiation visible light. The electromagnetic spectrum is made up of gamma rays, x-rays, ultraviolet light, visible light, infrared radiation, microwaves, TV, and radio signals.