Physics
Work and Power
Quick fact
A person can produce about 100 watts of sustained power—enough to light a bright bulb—while a car engine produces tens of thousands of watts.
Why this is interesting
You push a heavy box across the floor—but if it doesn't move, have you done any work? The answer might surprise you, and it all comes down to how physics defines work and power.
Read the full explanation
Understanding Work and Power
In everyday language, work means effort. In physics, work has a precise definition: it is done when a force acts on an object and causes it to move in the direction of the force. If you push against a wall and it doesn’t budge, no work is done—no matter how tired you feel. Work is calculated as force multiplied by the distance moved (in the direction of the force). The unit of work is the joule (J). Power, on the other hand, is the rate at which work is done—how much work per second. A powerful machine does the same amount of work as a weaker one, but in less time. The unit of power is the watt (W), equal to one joule per second. Think of it like this: work is the total energy transferred; power is how fast that transfer happens.
A deeper explanation
At its core, work represents energy transfer. When you do work on an object, you change its energy—increasing its kinetic energy if you speed it up, or its potential energy if you lift it. The work-energy theorem states that the net work done on an object equals its change in kinetic energy. Power connects work to time, making it crucial for efficiency and practical applications. For example, an engine rated 200 kW can do 200,000 joules of work each second. Understanding power helps explain why climbing stairs quickly is more exhausting than slowly—you're outputting more power. In machines, power losses due to friction reduce efficiency. Work and power are not just academic; they govern every mechanical process, from the hum of a ceiling fan to the thrust of a rocket.