The watt

The watt (W) is the modern scientific unit of power. One watt is the power when energy is transferred at the rate of one joule per second.

1 watt =  1 joule
              1 second

For example, what is the power of a car engine that can increase the kinetic energy of a car by 3 000 J in 0.5 s?

power = energy transferred
                  time taken

           =  3000
                 0.5

           = 6 000 W, or 6.0 kilowatts (kW).