Reaction time (ruler drop) sim
Line up a 50 cm rule with the catcher's thumb, drop it, read the catch on a magnified scale, convert it to a reaction time, take ten repeats and a mean, spot the anomaly, and compare practice, distraction, caffeine and alcohol on a bar chart of your own means.
Measuring reaction time by the ruler drop: catch distance to time with t = √(2d / g), repeats and means, anomalies, control variables, and the effects of practice, distraction, caffeine and alcohol (a depressant) · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Reaction time by the ruler drop: a model of AQA required practical 7. A partner holds a 50 cm rule with its 0 mark level with the top of the catcher's thumb and lets go at a random moment (a seeded wait of 1.0 to 4.0 s). The rule falls freely, so the distance fallen is d = ½ g t² and the reaction time is t = √(2d / g), with g = 9.8 m/s² and d in metres. A 50 cm rule is used so every model catch fits on it; the model's limits are 0.171 and 0.309 s, and its actual times lie between 0.178 and 0.292 s (a 30 cm ruler only times catches up to 0.25 s). Anomaly rule used here: a reading is an anomaly if its time is more than 25 % away from the median of that condition's ten readings; it is left out of the mean. The effects of practice, distraction, caffeine and alcohol are illustrative: the real effects differ, and vary from person to person. Simplified on purpose: illustrative numbers; the reaction times are seeded, so the same drops always give the same catches; no air resistance on the rule; the rule falls straight down without turning or rubbing on the fingers; the fingers close the moment the reaction time ends (closing is part of the time); the reaction time includes seeing, the nerve impulses, the brain deciding and the muscles moving (the whole response, not a reflex); each catch lies exactly on a millimetre mark; the fall is shown 6 times slower than real time; one catcher, so the results say nothing about other people.
- Lit: the 50 cm rule, the part to watch
- Magnified scale: the rule at the top of the thumb
- Read the mark level with the top of the thumb
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