Momentum and its conservation
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why a rifle kicks back
- What is momentum?
Read the transcript of the teaching part
Last time
Before we start: last time, in Motion quantities and graphs, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why a rifle kicks back
Fire a rifle, and the bullet shoots forwards, but the rifle jerks backwards into your shoulder. Nothing pushed from outside, yet both gained motion. The secret is a quantity that is passed between the two but never lost: momentum.
What is momentum?
Linear momentum is the product of mass and velocity: p equals m v. It is a vector, with the same direction as the velocity. The unit is kilogram metre per second, which is also newton second. A heavy lorry and a light car at the same speed: the lorry has more momentum, because its mass is bigger. Momentum is not force times time by definition. Force times time is the change in momentum, called impulse.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Conservation of momentum · Conservation of momentum.
Chapter 3.1: Dynamics
- Momentum and its conservation 5 min
- Newton's laws and force as rate of change of momentum 5 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.