Power, in physics, is the rate at which work is done or at which energy is delivered. From the perspective of physics, work is done when a force moves an object.
A task requires the same amount of work or energy whether it is done quickly or slowly. But the faster the task is done, the greater the power required. For example, to push a load of bricks 10 feet in 10 seconds takes twice as much power as does pushing the same load the same distance in 20 seconds. Increasing the speed of a particular automobile from 0 to 60 miles per hour requires essentially the same amount of work no matter how rapidly the car accelerates. But cars with more powerful engines reach 60 miles per hour more quickly.
Power can be calculated with the following formula:
In the formula, P stands for power, W for work, and t for time. The amount of work done equals the product of the force and the distance the object moves in the direction of the force. Therefore, the formula for power can also be written:
Here F stands for force and d for distance.
In systems of measurement, power is typically expressed in units of work divided by units of time. The basic unit of power in the metric system is the watt. A watt is the power required to perform one joule of work per second. A joule of work is done when 1 newton of force moves an object 1 meter (see Newton ). For example, if 100 newtons of force are used to lift an object 2 meters, the work done equals 200 joules. If the work is performed in 4 seconds, the power used is 50 joules per second, or 50 watts:
In the English system of units, power is often measured in horsepower. One horsepower equals 745.700 watts.
Electric current does work, and electric power is a measure of the amount of electric energy which is delivered per unit time. For example, a 60-watt light bulb requires 60 joules of energy each second, or 60 watts of electric power, to operate. A 120-watt light bulb requires twice as much power. Electric power used in the home is often measured in kilowatts (thousands of watts).
