GCSE Physics · Edexcel 1PH0 · Topic 9B
Moments, levers and gears
Key points
- The moment of a force is its turning effect: , where is the perpendicular distance from the pivot to the line of the force. Unit: N m.
- Principle of moments: in equilibrium, total clockwise moments = total anticlockwise moments.
- A longer lever means a smaller force is needed to produce the same moment, e.g. spanners and crowbars.
- Gears pass turning effects between shafts. A small gear driving a large gear turns the large one more slowly but with a bigger moment.
- A large gear driving a small gear makes the small one turn faster with a smaller moment.
- Meshing gears turn in opposite directions.
Topic notesPremium
Forces can make things turn as well as move. Doors, spanners, seesaws, wheelbarrows and bicycle gears all depend on the turning effect of a force, called its moment.
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