Reaction Time Virtual Lab: The Ruler Drop Test

Updated 2026-10-07

This reaction time virtual lab follows the AQA GCSE required practical on human reaction time. Students first catch a falling ruler themselves and convert each drop distance into a time with t = √(2d/g). Then they switch to a simulated class of up to 40 students and compare four factors: seeing or hearing the cue, the dominant or non-dominant hand, being focused or distracted, and no caffeine or caffeine. They come away with means, ranges and anomalies, and a clear sense of why one person's single result proves nothing. Every class-data number below was read from the simulation.

Reaction time – the ruler drop test

Curriculum links

AQA GCSE Biology: specification 4.5.2.1, structure and function of the nervous system, and the required practical on the effect of a factor on human reaction time. The combined science course has the same practical.
NGSS: MS-LS1-8, sensory receptors respond to stimuli by sending messages to the brain.
Simulic is not affiliated with or endorsed by the College Board or AQA.

Before the lab (5 min)

Ask: "Students catch the ruler while counting back from 100 in sevens. How will their mean reaction time compare with catching while focused?" Students choose longer, shorter, or the same, and write one reason. On a class link this is question 1; the simulation unlocks after they answer.

Method in the simulation

Part 1: your own reaction time (10 min).

Keep Mode: Test your own reaction time, Stimulus: See the ruler fall, Dominant hand, Ruler 50 cm, 5 trials.
Tap the picture or press the space bar. The ruler drops at a random moment; catch it as soon as it moves.
Record d and t for each trial. Click a row to see the d → t working. Repeat with the non-dominant hand.

Your own times include the delay of the screen and the mouse or touchscreen, so compare them only with each other.

Part 2: the simulated class (20 min).

Press Reset. Choose Mode: Simulated class data, Students 20, Trials per condition 5, Ruler 50 cm. Do not press New class, so every student sees the same data.
For each option in Compare, record the mean t of A and B and the mean difference B − A.
Choose Compare: No caffeine vs caffeine, Students 5, Trials 2, and press Reset. Record the difference B − A, press New class, and record again: five classes in all. Then repeat with Students 40 and Trials 10.

Compare	Mean t, A (s)	Mean t, B (s)	B − A (s)	Students faster in B
Seeing vs hearing
Dominant vs non-dominant
Focused vs distracted
No caffeine vs caffeine

class data, Focused vs distracted, with the means chart and summary table

Expected results

After Reset, with 20 students, 5 trials and a 50 cm ruler, condition A gives a mean t of 0.230 s (range 0.188–0.265 s, mean d 26.3 cm) for every comparison, because the same students do it each time. Condition B:

hearing a click: 0.200 s, a difference of −0.030 s; 17 of 20 students are faster;
non-dominant hand: 0.233 s, +0.003 s; only 7 of 20 are faster, so there is no clear effect;
distracted: 0.259 s, +0.029 s; only 3 of 20 are faster;
caffeine: 0.214 s, −0.016 s; 15 of 20 are faster.

Caffeine with 5 students and 2 trials gives a different answer each time. Starting from Reset, five classes gave +0.003, −0.016, −0.026, −0.004 and −0.011 s, so one class even shows caffeine making students slower. With 40 students and 10 trials, five classes all gave between −0.008 and −0.013 s.

Questions for students

Prediction: how will the mean reaction time of distracted students compare with focused students?
Which of these must stay the same in a fair ruler-drop test?
A ruler is caught after falling d = 21.5 cm. Calculate the reaction time.
Class data, Focused vs distracted: calculate the percentage increase in mean t.
Compare caffeine data from 5 students × 2 trials with 40 students × 10 trials. Explain why a conclusion needs many trials and many people.

Answers for teachers:

Longer: the brain is busy with another task.
The starting position of the ruler, with the 0 mark level with the top of the thumb.
t = √(2 × 0.215 ÷ 9.8) = 0.209 s (accepted ± 0.002).
(0.259 − 0.230) ÷ 0.230 × 100 = 12.6 % (accepted ± 1).
The effect is about 0.01 s, much smaller than the trial-to-trial and person-to-person variation. Small samples give differences of +0.003 to −0.026 s. Large ones agree closely, so the mean is repeatable.

Common misconceptions

"Catching the ruler is a reflex." It is a conscious response through the brain, so it is slower than a reflex and improves with practice.
"Twice the distance means twice the time." d = ½gt², so twice the time means four times the distance.
"My fastest catch is my reaction time." A catch under 0.10 s is a guess; the simulation flags it and leaves it out of the mean.
"A device timer is as good as a real ruler." The screen and input add delay, which the simulation notes as about 0.02–0.08 s.

Extension

Practice effect. Set Chart: By trial number (practice) with 10 trials. The first trials are slower; ask why the simulation makes half the class do A first.
Ruler length. Ask what the longest time a 30 cm ruler can measure is: √(2 × 0.30 ÷ 9.8) ≈ 0.25 s. Ask why slower students need the 50 cm ruler.

FAQ

Why do the questions use the class data, not the student's own times?

Each student's own times are different, and a device adds its own delay. The class data are the same for everyone after Reset, so answers can be marked automatically.

Is the caffeine condition ethical?

It is simulated data only, which is why it is in the simulation. Students should not be given caffeine for a school experiment.

Does this replace the wet lab?

Not for AQA: required practicals must still be done by hand. Use the simulation to plan the test, practise the d → t conversion and analyse a large dataset. See virtual labs vs physical labs.