Definition · Plain-language
Work in physics
In physics, work is the energy transferred when a force moves an object through a distance in the direction of the force.
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Force acting over a distance
In the everyday sense, "work" means effort, but in physics it has a precise meaning: work is done only when a force moves something. Specifically, work equals the force multiplied by the distance the object moves in the direction of that force. Lifting a box does work against gravity; pushing a trolley does work against friction. If you push against a wall that does not move, you may tire, but in the physics sense you have done no work at all, because nothing was displaced.
Work as energy transfer
Work is fundamentally about energy. Doing work on an object transfers energy to it, and the amount of work done equals the energy transferred, which is why both are measured in the same unit, the joule. Lifting an object gives it gravitational potential energy; pushing it along gives it kinetic energy. This link is captured by the work–energy principle: the net work done on an object equals the change in its kinetic energy. Work is therefore the mechanism by which forces add or remove energy from a system.
When direction matters
Only the part of a force that lies along the direction of motion does work. A force at right angles to the movement does no work at all, which is why the gravitational force on a satellite in a circular orbit does no work — it always pulls sideways to the motion. When a force opposes the motion, such as friction, it does negative work, removing energy from the object. Carefully accounting for direction is essential to calculating work correctly.
Key facts
At a glance
- Definition: energy transferred when a force moves an object a distance
- Formula: work = force × distance moved in the force’s direction
- SI unit: the joule (J)
- No movement: no work is done if the object does not move
- Work–energy: net work equals the change in kinetic energy
- Direction: only the force component along the motion does work
Common misconceptions
What people often get wrong
Often heard: Holding a heavy object still does work in physics.
Actually: Holding something steady involves no movement, so no work is done in the physics sense, however tiring it feels. Work requires the object to move through a distance.
Often heard: Any force on a moving object does work.
Actually: Only the part of a force along the direction of motion does work. A force acting at right angles, such as gravity on a circular orbit, does no work even though the object moves.
Often heard: Work and power are the same thing.
Actually: Work is the energy transferred, measured in joules; power is how quickly that work is done, measured in watts. Doing the same work faster requires more power, not more work.
Going deeper
