Brainlag PlusThinking distance and braking distance, what changes each, reaction times from a ruler drop, and why braking distance goes with speed squared.
Two distances, added
When a driver sees a hazard, the car keeps going while the driver reacts, then slows down once the brakes are on.
stopping distance = thinking distance + braking distance
thinking distance = speed × reaction time
Typical reaction times are 0.2 s to 0.9 s. Tiredness, alcohol, drugs and phones make them longer, so they change the thinking distance. Wet or icy roads and worn tyres or brakes change the braking distance.
Speed changes both. That is why the speed limit near a school matters so much.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 4, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- The Newton's second law simulation beside every question
- Anything you get wrong is saved to your flashcards