This how it works covers Why Braking Distance Scales with v²: The Energy Connection within Stopping Distances for GCSE Physics. Revise Stopping Distances in Forces for GCSE Physics with 15 exam-style questions and 5 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ Why Braking Distance Scales with v²: The Energy Connection
The key to understanding why braking distance quadruples when speed doubles lies in kinetic energy. KE = ½mv². When you brake, the braking force transfers ALL the kinetic energy away (converting it to thermal energy in the brakes and tyres).
Work done by brakes = braking force × braking distance = KE = ½mv²
If the braking force is constant (same brakes, same road conditions): braking distance = mv² / (2 × braking force). Since braking distance is proportional to v², doubling the speed quadruples the braking distance.
This is why modern cars have ABS (Anti-lock Braking Systems) — by preventing wheel lock-up, maximum friction is maintained throughout braking, minimising stopping distance.
Practice questions for Stopping Distances
What is the correct definition of stopping distance?
Explain why a car travelling at higher speed has a greater braking distance than a car travelling at lower speed, assuming the same braking force.