Impulse & Collisions

PhysicsAQAGCSEUnit: Forces
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The basics

Why Crumple Zones Save Lives

📖 Why Crumple Zones Save Lives

Imagine catching a cricket ball. If you catch it with rigid hands, it HURTS! But if you let your hands move backwards with the ball, it's much gentler. Why? The ball's momentum change is the same either way — but by increasing the TIME over which you stop it, you reduce the FORCE. This is impulse, and it's why cars have crumple zones, cyclists wear helmets, and gymnasts land on springy floors!
Impulse Equation (Higher Tier)
F × t = m × Δv = Δ(mv)
Impulse (N s) = Change in momentum (kg m/s)
Spotlight
Understanding Impulse

Definition: Impulse is the change in momentum of an object, which equals force × time.

Exam tip

Earn the mark scheme marks

🎯 Exam Focus — Impulse and Collisions

Frequently Examined

Impulse is examined on Edexcel 1PH0/1 (Paper 1, Higher tier — 1PH0/1H). Edexcel presents this topic through real-world safety scenarios ("A car travelling at 12 m/s is brought to rest in 0.8 s…") and asks students to apply F = Δp/t. Key question types:

  • Calculate impulse — use F × t = Δp; show both the momentum change and the impulse value
  • Calculate average force from impulse — rearrange to F = Δp/t, link to safety features
  • Explain why safety features reduce injury — increasing time of impact reduces force for the same momentum change
  • Elastic vs inelastic collision distinction — state which quantity is conserved in each
  • Force-time graph questions — area under graph = impulse; interpret shape of graph

Edexcel style note: Edexcel frequently uses "Suggest" command word for novel safety scenarios — apply the same impulse principle even if the context is unfamiliar (helmet, airbag, crumple zone, catching a ball).

Now try it yourself

Quiz · Question 1 of 13

Which equation correctly defines impulse?

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