One Definition of Power
When we discussed the transformation and transfer of energy, we learned about two ways in which energy can be changed. We learned that energy can be transformed from one kind to another. For instance, gravitational potential energy is transformed to kinetic energy for a falling object. We also learned that energy can be transferred from one object (or system) to another. For example, when you hit a baseball with a baseball bat, kinetic energy from the baseball bat is transferred to the baseball.
Power is just defined as the rate at which energy is transformed from one form into another or the rate at which energy is transferred from one system to another. In other words, power is is related to how quickly energy is transformed from one form into another or transferred from one object to another.
One formula for power is shown at the right. Because power is the rate at which energy is transformed or transferred, the formula for power is change in energy divided by time. The change in energy in the formula can be the amount of energy which is transformed into another kind or the amount of energy which is transferred from one object (or system) to another.