Revision notes · Forces
Work done and energy transfer
Work done and energy transfer4.5.2
Definition: Work is done on an object whenever a force causes it to move. Doing work always transfers energy — from whatever is exerting the force to the object (or into another store, such as heat).
| Equation | Units |
|---|---|
| work done = force × distance — W = F × s | W in joules (J), F in newtons (N), s in metres (m) |
The distance s is the distance moved along the direction of the force. If a book is lifted 1 m straight up, work is done against gravity over that 1 m — even if the book was also carried 2 m sideways at the same time, no work is done against gravity for that sideways motion, because gravity doesn't act sideways.
Definition: One joule of work is done when a force of one newton causes a displacement of one metre in the direction of the force: 1 joule = 1 newton-metre.
🧠 Remember: Work done against friction (or other resistive forces) doesn't disappear — it's transferred to the thermal energy stores of the objects involved, raising their temperature. This is why rubbing your hands together, or a car's brakes, get warm.
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