The push or pull needed to move something is called

*force*and the work done is the force times the distance the object is moved. Power = work/time.

If a boy weighing 80 pounds climbs 20 feet up a ladder, 1600 ft-lbs. of work is done against gravity. The force the boy needs to climb the ladder equals his own weight. If the boy climbs the ladder in 4 seconds, the power =

**1600 ft-lbs/4. or 400 ft.lbs per sec**. If he takes 8 seconds to climb, the power is less. Power =

**1600/8 or 200 ft-lbs. per sec**.

Thus power is the time rate of doing work.

Power may be expressed in many different units such as

*horsepower*and

*watts*(

*joules*per second). When the time rate of working is 550 ft-lbs. per second (or 33,000 per minute) the power is one horsepower. The watt rating on an electric light bulb gives the rate at which electrical energy (work) will be consumed when the bulb is used. The 100 watts means 100 joules per second. This is a unit of power MEASUREMENT in the metric system.