We all have an intuitive idea of what this means. We might also recognize that heat, electricity, and light have energy as well. Energy of motion is called kinetic energy . For example, a car travelling at 90 mph has much more energy than a baseball travelling at 90 mph. A different type of energy is potential energy , which can be defined for all of the fundamental forces.
Potential energy is basically another way of describing the effect of a force.
Consider an object which experiences a gravitational force. If the object is thrown upward, it will have some initial speed but it will immediately begin to slow down and eventually stop, i.e. its kinetic energy decreases . The object will then begin to move back downward, rapidly gaining speed as it is accelerated by gravity, and its kinetic energy increases . We associate potential energy with the object's height, and we say that its potential energy increases as it rises, and decreases as it falls. If kinetic energy increases, potential energy must decrease by an equal amount, and vice versa, so that E remains a constant value.