Energy can be defined as the capacity to do work or accomplish a physical action like running, while power is the rate at which energy is transmitted or work is done. The unit of measurement for energy is Joules, calories or ergs. Power's unit of measurement is Watts, which is ergs per second or Joules per second.
Some of the different forms of energy include: elastic, light, sound, electromagnetic, gravitational, thermal, potential and kinetic energy. The most widely known form of power is electrical power, which is the rate at which electrical energy is transmitted by a closed circuit. Other forms of power may include optical power and human power.
Energy can be converted from one form into another. For example, a battery produces electrical energy after converting it form chemical energy. The process of chemical explosion converts chemical energy into thermal and kinetic energy. Power cannot be transformed or converted.
Since power is an instantaneous quantity, it cannot be stored. Energy is available in a time component and can therefore be stored for future use. Levers reduce the amount of energy required to accomplish tasks, but they are typically described by their power rating. Powerful levers are more efficient.