Reaction time and stopping distance: the ruler drop and the test track sim
Line up a metre rule, catch it the moment your partner lets go, read the catch distance and turn it into a reaction time with a conversion graph, five times alert and five times distracted; then drive a car on a test track at 10 to 40 m/s with your own reaction time, on dry, wet or icy roads, worn or good tyres and brakes, empty or full, and plot stopping distance against speed and braking distance against speed squared.
Dynamics · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Model: the rule falls freely, d = ½ g t² (g = 10 N/kg; not a syllabus equation: it follows from v² = 2as and a = Δv ÷ t), so the catch distance gives the reaction time. Stopping distance = thinking distance (speed × reaction time) + braking distance (v² ÷ 2a), where the deceleration a is the smaller of the brakes' largest force ÷ mass and the tyres' grip μ g. Your own presses include the screen's small delay; a classmate's times are a seeded model (0.21 s, distracted 0.30 s). Grip, brake force, mass and the extra thinking time are illustrative. Idealised: no air resistance on the rule, one steady deceleration, a level road.
- The metre rule: the part to watch
- Lab bench with a gas tap, the catcher's and the partner's hands, phone, sticky note, notebook and pencil, conversion chart, spare stool
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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