GCSE Physics · AQA 8463 · Topic 4.5.4
Moments, levers and gears
Key points
- A moment is the turning effect of a force: , where is the perpendicular distance from the pivot to the line of action of the force. Units: N m.
- Principle of moments: if an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment.
- A longer lever lets a small force produce a large moment, so it acts as a force multiplier (spanners, crowbars, wheelbarrows).
- Gears transmit rotation. A small gear driving a larger gear makes the large gear turn more slowly but with a larger moment.
- Exam tip: always measure the distance to the pivot, not between the forces.
Topic notesPremium
A force can make something turn as well as move. Opening a door, using a spanner, balancing a see-saw and changing gear on a bike all depend on the turning effect of a force, called its moment.
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