AQA · Physics · 8463
GCSE Physics: Moments, levers and gears
Forces · AQA GCSE Physics (8463), specification point 4.5.4. Cards are generated from the exam board's own specification for "Moments, levers and gears", and every card links back to the page it came from. Separate science only. Specification © AQA — used with attribution.
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What is the turning effect of a force called?
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The moment of the force.
What is the equation for the moment of a force?
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M = F × d (moment = force × perpendicular distance from the pivot to the line of action of the force).
What is the unit of the moment of a force?
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Newton-metres (Nm).
In M = Fd, how is the distance d measured?
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As the perpendicular distance from the pivot to the line of action of the force, in metres.
What condition must moments satisfy for an object to be balanced?
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The total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
For a balanced object, the total clockwise moment equals the total ? moment about the same pivot.
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anticlockwise
A 20 N force acts 0.5 m perpendicular from a pivot. What is the moment?
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10 Nm (M = 20 N × 0.5 m).
A see-saw balances with 300 N at 1.5 m on one side. What force is needed 0.5 m from the pivot on the other side?
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900 N (300 × 1.5 = F × 0.5, so F = 450 ÷ 0.5).
Name two simple systems used to transmit the rotational effects of forces.
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A simple lever and a simple gear system.
How does a lever act as a force multiplier?
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Applying a small force far from the pivot creates a large moment, which can lift a heavy load close to the pivot (moments are balanced: F₁d₁ = F₂d₂).
How does a small gear driving a larger gear change the turning effect?
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The larger gear turns more slowly but with a greater moment, because the same force acts at a larger radius.
When two gears mesh, in which direction does the driven gear rotate relative to the driver?
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In the opposite direction.
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