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Moments, levers and gears
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A force can make an object turn. Levers and gears use moments to make work easier. Separate Physics only.
Moments
moment = force × perpendicular distance from the pivot, M = F × d
Unit: N m.
Unit: N m.
The principle of moments
If an object is balanced: total clockwise moment = total anticlockwise moment.
A 300 N child sits 2 m from a seesaw pivot. To balance, a 400 N child sits at 600 ÷ 400 = 1.5 m on the other side.
A 300 N child sits 2 m from a seesaw pivot. To balance, a 400 N child sits at 600 ÷ 400 = 1.5 m on the other side.
Levers and gears
Levers increase the turning effect: a long handle means less force is needed.
Gears transmit turning effects. A small gear driving a big gear: the big gear turns more slowly but with a bigger moment.
Gears transmit turning effects. A small gear driving a big gear: the big gear turns more slowly but with a bigger moment.
A 20 N force acts 0.3 m from a pivot. Find the moment.
- M = 20 × 0.3
Answer: 6 N m
Moment = force × perpendicular distance. Balanced: clockwise moments = anticlockwise moments. Longer levers and larger driven gears give bigger turning effects.
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