GCSE Physics: Newton's Laws and Stopping Distances

Newton's three laws are the explanatory core of GCSE forces, and the specification pairs them with their most consequential everyday application: how far a car travels before it stops. This quiz covers both halves.

The first law is tested through its exam signature: a car at constant velocity on a straight road has a resultant force of exactly zero — not a small forward force, zero. The second law is applied numerically in both directions, finding the 20,000 N force accelerating a 5000 kg rocket at 4 m/s² and the 4 m/s² acceleration of a 1500 kg car under 6000 N, plus a scenario question about what a net force does to an object already moving. The third law gets the treatment its most common misconception demands: genuine action-reaction pairs act on different objects — a swimmer pushing water, a balloon expelling air — and the distractors include the balanced-forces-on-one-object cases that are not third-law pairs. Inertia is defined precisely as the tendency to continue in the existing state of motion.

The stopping-distance half applies the framework to road safety exactly as papers do. Stopping distance decomposes into thinking distance plus braking distance (12 m + 24 m = 36 m), and thinking distance is calculated as speed times reaction time for a driver at 30 m/s with a 0.5 s reaction. The factor-sorting questions enforce the split the mark schemes reward: tiredness, alcohol and distraction lengthen thinking distance by slowing the driver, while wet roads, worn brakes and worn tyres lengthen braking distance by weakening the physics of deceleration. Typical reaction times of 0.2–0.9 s are covered as required. Every explanation names the law or principle doing the work.

• Apply Newton's first law: zero resultant force at constant velocity
• Use Newton's second law to find force or acceleration from given values
• Identify genuine Newton's third law action-reaction pairs
• Split stopping distance into thinking and braking distance and calculate each
• Sort factors by whether they affect thinking distance or braking distance

Topic scope follows the Forces section of the Department for Education's GCSE combined science and physics subject content: Newton's first, second and third laws, inertia, and the factors affecting stopping distance, thinking distance and braking distance including typical reaction times. Reflects the 2025–2027 equations sheet arrangement.