Kinetic and potential energy

Energy can exist in either of two main forms. Kinetic energy is the kind you probably think of right away when you imagine energy. A person running, a car moving down a freeway, a speeding aircraft, a chamber of superheated gas—all these things are visible manifestations of kinetic energy, or energy in action. The dissipation of electrical power, over time, is a form of kinetic energy too.
Potential energy is not as vividly apparent. When you raise a block of concrete into the air, you are creating potential energy. You remember the units called foot pounds, the best way to measure such energy, from school physics classes. If you raise a one-pound weight a foot, it gains one foot pound of potential energy. If you raise it 100 feet, it gains 100 foot pounds. If you raise a 100-pound weight 100 feet, it will gain 100 × 100, or 10,000, foot pounds of potential energy. This energy becomes spectacularly evident if you happen to drop a 100-pound weight from a tenth-story window. (But don’t!)