Stopping Distances and Braking Energy
Stopping distance splits into thinking distance, set by reaction time and speed, and braking distance, set by the work the brakes must do to empty the kinetic store. Braking distance grows with the square of the speed.
What a learner can do afterwards
- Calculates thinking distance from a reaction time and a speed
- Uses the kinetic store and the braking force to work out a braking distance
- Explains why doubling the speed roughly quadruples the braking distance, and lists what makes each part longer
1 · Read
Stopping distance splits in two for you. Thinking distance is the ground covered while you notice danger and react, before your foot touches the brake. Braking distance is the ground covered while the brakes drain the kinetic store to zero.
Thinking distance is speed times reaction time. At 20 m/s with a 0.6 s reaction, you travel 20 times 0.6 = 12 m before braking even starts. Tiredness, distraction, and drink stretch the reaction, and higher speed covers more ground in the same time.
Braking distance comes from work: brake force times distance = kinetic store removed. Since the store grows with speed squared, doubling speed from 15 m/s to 30 m/s roughly quadruples the braking distance. Worn brakes, worn tyres, wet roads, and heavy loads all stretch it further.
Answer stopping questions in three beats: thinking distance, braking distance, then the total. Say which part each factor touches: phones and drink hit thinking, rain and bald tyres hit braking.
Reaction times speed for thinking, speed squared for braking, and the total is both added.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.