5.1.4 Power

• The power of a machine is the rate at which it transfers energy
• Since work done is equal to the energy transferred, power can also be defined as the rate of doing work or the work done per unit time
• The SI unit for power is Watts (W) where 1 W = 1 J s^-1

Power is the rate of change of work

• You may be familiar with labels on lightbulbs which indicate their power such as 60 W or 100 W. These tell you about an energy transferred by an electrical current rather than by a force doing work