GCSE Physics · AQA 8463 · Topic 4.5.6
Forces and motion
Key points
- Speed: . Typical speeds: walking 1.5 m/s, running 3 m/s, cycling 6 m/s, sound in air 330 m/s.
- Acceleration: (m/s²). Uniform acceleration: . Objects near Earth fall at about 9.8 m/s².
- Distance–time graph gradient = speed. Velocity–time graph gradient = acceleration; area under it = distance travelled.
- Newton's first law: zero resultant force means constant velocity (or at rest). Second law: . Third law: interacting objects exert equal and opposite forces on each other.
- Terminal velocity is reached when air resistance balances weight.
- Stopping distance = thinking distance + braking distance. Reaction time (0.2–0.9 s) is affected by tiredness, drugs, alcohol and distractions; braking distance by speed, wet or icy roads and worn tyres or brakes.
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This is the core of mechanics: describing motion with numbers and graphs, then explaining it with Newton's three laws. It finishes with a real-world use, the stopping distance of a car.
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