Power is the rate at which work is done or energy is transferred. It is measured in watts. One watt is one joule per second. A 100-watt bulb uses 100 joules of energy every second. A 1,000-watt microwave uses 1,000 joules per second. Power is not the same as energy. Energy is the total amount. Power is how fast it is used or produced. A 100-watt bulb running for 10 hours uses 1 kilowatt-hour of energy. A 1,000-watt microwave running for 1 hour uses the same amount.

Power comes in many forms. Mechanical power is the rate at which work is done by a force. Electrical power is the rate at which electrical energy is transferred. It is calculated as P = VI, where V is voltage and I is current. Thermal power is the rate at which heat is transferred. Human power output varies. A person can produce about 100 watts of sustained mechanical power, and up to 1,000 watts for short bursts. A car engine produces about 100,000 watts. A large power plant produces billions of watts. Power is a key concept in physics, engineering, and everyday life. It determines how fast a device can do its job, and how much energy it consumes.

Power facts

• Definition. Rate of work or energy transfer.
• Unit. Watt (W) = joule per second.
• Electrical. P = VI.
• Mechanical. P = Fv.
• Human. About 100 watts sustained.

Power is not the same as force. Force is a push or pull. Power is the rate at which force does work.