AQA · Physics · 8463
GCSE Physics: Changes in momentum
Forces · AQA GCSE Physics (8463), specification point 4.5.7.3. Cards are generated from the exam board's own specification for "Changes in momentum", and every card links back to the page it came from. Higher tier only. Separate science only. Specification © AQA — used with attribution.
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What happens to an object's momentum when a force acts on it?
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A change in momentum occurs (this applies whether the object is moving or able to move).
What equation gives force in terms of change in momentum?
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F = mΔv / Δt
Force equals the ? of momentum.
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rate of change
Which two equations combine to give F = mΔv / Δt?
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F = m × a and a = (v − u) / t.
In F = mΔv / Δt, what does mΔv represent?
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The change in momentum.
Why does an air bag reduce injury in a collision?
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It increases the time over which the momentum changes, reducing the rate of change of momentum and so the force on the person.
How does a crash mat reduce the force on a falling gymnast?
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It lengthens the time taken for the momentum to change to zero, so the rate of change of momentum (the force) is smaller.
How does a cycle helmet protect the head in an impact?
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Its cushioning increases the time taken for the head's momentum to change, reducing the force on the skull.
Why are playground surfaces cushioned?
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A cushioned surface increases the time over which a falling child's momentum changes, lowering the force of the impact.
For a fixed change in momentum, how does increasing the collision time affect the force?
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The force decreases, because F = mΔv / Δt — a larger Δt gives a smaller F.
Why is F = mΔv / Δt not required to be memorised in the exam?
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It is given on the Physics Equation sheet; students must be able to apply it.
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