Reaction Time and Stopping Distance
Stopping distance = reaction distance + braking distance.
About this topic
The total stopping distance of a vehicle is the thinking (reaction) distance plus the braking distance. Reaction distance = speed × reaction time, about 0.7 s for alert drivers, and braking distance grows with the square of speed: doubling speed quadruples it.
The braking part comes from v² = u² + 2as, so the distance is u²/(2a) when stopping with deceleration a. A typical car on dry road decelerates at about 7 to 8 m/s². Example: at 20 m/s (72 km/h) the thinking distance is 14 m and braking is about 27 m for a total of roughly 41 m. At 30 m/s the thinking distance is 21 m and the braking distance about 60 m.
Tiredness, alcohol, distractions such as phones, wet roads, worn tyres and heavy loads all lengthen stopping distance. This is why speed limits are reduced near schools and in bad weather, and why a following gap of at least two to three seconds is recommended.
Misconception: braking distance does not simply double when speed doubles; it quadruples. Even a small speed increase has a big effect on how much space you need and how severe a crash would be.
Key ideas
- Reaction distance = v × reaction time
- Braking distance grows with v²
- Wet roads increase braking distance
Quick check
Use cases: where Reaction Time and Stopping Distance helps
- Homework: review the key idea behind Reaction Time and Stopping Distance before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Reaction Time and Stopping Distance without notes.
- Visual learning: play with the interactive lab to see how Reaction Time and Stopping Distance changes when you adjust its inputs.
- Teaching a friend: explain Reaction Time and Stopping Distance in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Reaction Time and Stopping Distance?
Stopping distance = reaction distance + braking distance.
What will I learn in Reaction Time and Stopping Distance?
Reaction distance = v × reaction time. Braking distance grows with v². Wet roads increase braking distance.
Is Reaction Time and Stopping Distance part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Reaction Time and Stopping Distance lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Reaction Time and Stopping Distance?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.