Even light itself is only one kind of energy.
Energy is nothing more than the ability for something to do work.
If I hold a hammer above the ground, its speed is zero, but it has a lot of 'potential energy' which is invisible, un til I release the hammer. Then this 'potential energy' is steadily transfered into kinetic energy and this is 100 percent complete at the instant before the hammer strikes the ground. Pure' energy is a vague term that doesn't have much of a physical meaning to it. Return to the Ask the Space Scientist main page.