GCSE Physics · AQA 8463 · Topic 4.5.7

Momentum

Key points

(Higher tier) Momentum: $p = mv$ , units kg m/s. Momentum is a vector.
In a closed system, total momentum before an event equals total momentum after it: conservation of momentum.
In an explosion from rest, total momentum is zero both before and after, so the parts move off in opposite directions.
(Separate physics) Force equals rate of change of momentum: $F = \frac{m\Delta v}{\Delta t}$ .
Increasing the time of an impact reduces the force. Air bags, seat belts, crumple zones, cycle helmets and crash mats all work this way.

Topic notesPremium

(Higher tier) This whole sub-topic is Higher tier only. Momentum explains what happens in collisions and explosions, from snooker balls to rockets, and why car safety features save lives by making crashes last longer.

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