Simulic
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Reaction time – the ruler drop test

BiologyHuman & Animal PhysiologyAges 16–17

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Measure reaction time with the ruler drop test. Test yourself: the ruler is released at a random moment and you catch it with a tap or a key press when you see it fall or hear a click; read the drop distance d off the scale and convert it step by step to t = √(2d/g), with early presses rejected. Simulated class data: compare seeing with hearing, dominant with non-dominant hand, focused with distracted and no caffeine with caffeine, using trial tables, means, ranges, anomaly flags and charts of means, distributions and practice.

Lesson: Nervous system: reaction time and the ruler drop test

What it shows

Reaction time is the time between a stimulus and the response. In the ruler drop test one person releases a ruler and the other catches it between thumb and finger; the further it falls, the slower the reaction. The ruler falls freely from rest, so d = ½gt² and t = √(2d/g). The signal travels from the eye or ear along sensory neurons to the brain, then along motor neurons to the finger muscles. Catching is a conscious response, so it is much slower than a reflex and improves with practice. Results vary a lot from trial to trial, so repeats and means matter.

How to use

Choose a Stimulus and Catching hand, then tap the picture or press Ready. The ruler drops at a random moment: tap or press a key as soon as you see it fall, or hear the click. Read d in the zoom, check the d → t working, and repeat. Switch Mode to Simulated class data, pick what to Compare, and use Chart and New class.

Parameters you can change

  • Mode Test your own reaction time, Simulated class data
  • Stimulus See the ruler fall, Hear a click (eyes closed)
  • Catching hand Dominant hand, Non-dominant hand
  • Ruler length 30 cm, 50 cm, 100 cm
  • Trials per condition 1–10
  • Students in the simulated class 5–40
  • Compare (class data) Seeing vs hearing, Dominant vs non-dominant hand, Focused vs distracted, No caffeine vs caffeine (simulated)
  • Chart Mean for each condition, Histogram of t, By trial number (practice)

Questions to explore

  1. Why must the ruler be released at a random moment, and why are presses before it falls rejected?
  2. If a reaction time doubles, how does the drop distance change, and why?
  3. Why do you need many trials and many people to decide whether caffeine has an effect?

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