Energy Energy is the capacity to do work.
Energy can be in the form of thermal, radiant, electrical, mechanical, chemical, and atomic energy.
The first two come directly from the sun, the second two come indirectly from the sun , and the last two are independent from the sun. Historically, man first had himself and the sun to provide energy. He used himself to do any work and relied on the sun for a source of light and heat. Fire was the first usable energy discovery, and animals began to share some of the work. The use of coal to produce steam was a major breakthrough in man's development along with the industrial revolution - the age of the machine to do the work.