Moments

A moment is the turning effect of a force

A force, or several forces, can cause an object to rotate. The turning effect of a force is called its moment. The size of the moment of the force is given by:

M=Fd, Moment of a force=force x distance

• The force on the spanner causes a turning effect or moment on the nut. A larger force or a longer distance would mean a larger moment
• To get the maximum moment you need to push at right angles to the spanner. Pushing at any other angle means a smaller distance, and so a smaller moment

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Levers make it easier for us to do work

Levers increase the distance from the pivot at which the force is applied. Since M=Fd this means less force is needed to get the same moment. This means levers make it easier to do work

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Gears transmit rotational effects

• Gears are circular discs with ‘teeth’ around their edges
• Their teeth interlock so that turning one causes another to turn, in the opposite direction
• They are used to transmit the rotational effect of a force from one place to another
• Different sized gears can be used to change the moment of the force. A force transmitted to a larger gear will cause a bigger moment, as the distance to pivot is greater
• The larger gear will turn slower than the smaller gear

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