Question 1 (2 marks)
Method
Why should the ruler be dropped without warning?
Show model answer / marking points
To prevent anticipation of the stimulus (1), giving a fairer measurement of response time (1).
Required Practical 06: Reaction Time | AQA GCSE Science | The Science Department
About this practical and its aim
Aim
Investigate the effect of a chosen factor on human reaction time using a ruler-drop test.
Introduction
This is a very simple experiment that can be used to incorporate lots of other parts of biology and experimental science. You will basically drop a ruler through a student's open hand. When they see it fall, they grab it. This allows you to calculate means, spot anomalies, compare data and to even calculate time using S=ut + ½at2. You can also use this to test hypotheses like "does caffeine increase reaction rate?" and complete a double blind trial.
The science behind the practical
Reaction time includes sensing a stimulus, processing it and responding with muscles. A ruler-drop distance can estimate elapsed falling time.
Key things to remember
Keep hand and zero mark aligned; drop without warning; repeat measurements; compare means.
Equipment and apparatus
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Metre rule
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chair or desk
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results sheet
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calculator
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stopwatch optional
Method: How to carry out the experiment
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In groups, select a person to be the tester and the person to be tested.
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The tester holds a metre rule above the open hand of the person being tested. Both people should look at the hand of the person being tested so that there are no clues as to when the ruler is going to be dropped.
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The tester lets the ruler drop and the person being tested must close their hand around the ruler to catch it. The distance that the ruler falls (in cm) can be converted into seconds.
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Repeat this many times and record each reaction time into a table. Swap roles and repeat so that the reaction time of all students can be recorded.
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This experiment will allow you to look into the medical trial process too. Once everyone has a "baseline" result, everyone in the class can be given a drink. I provide two trays of drinks, one is diet cola and one is caffeine free diet cola (red cups and white cups. Students are not told which is which. Buy a cheap brand that does not have a distinctive taste - CHECK FOR ALLERGIES etc). After drinking a cup, I discuss that caffeine is supposed to speed up your reactions and students can see if they can work out which.
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When complete, look at how robust the method is and look at how it compares with a double blind trial.
Variables and fair testing
| Type of variable | What is measured or controlled? |
|---|---|
| Independent variable | Chosen factor, such as practice or distraction |
| Dependent variable | Distance fallen before catch, or calculated reaction time |
| Control variables | Same ruler; starting position; hand used; drop technique; participant where appropriate |
Safety and managing risks
Follow your teacher's instructions and your school's risk assessment. This page is not a substitute for a formal risk assessment.
| Hazard | Risk | Precaution |
|---|---|---|
Ruler-drop activity |
Fingers struck by ruler or collision |
Use a suitable lightweight ruler and clear working area. |
Human participants |
Discomfort, participation pressure or confidentiality issues |
Gain appropriate consent; allow opt-out; do not collect unnecessary identifying data. |
Results, calculations and analysis
Recording, presenting and interpreting results
Record repeated ruler distances (cm), identify anomalies and calculate mean distances or reaction times.
Calculations
For free fall from rest, time ≈ √(2 × distance in metres ÷ 9.81).
Conclusions, accuracy and evaluation
Drawing a conclusion
Shorter mean fall distance indicates faster reaction under comparable conditions.
Evaluating the investigation
Use repeated trials and a consistent release method; discuss anticipation, fatigue and practice effects.
More to learn
Ethical investigation
Allow voluntary participation and avoid routine caffeine-drink challenges. Practice or distraction is a suitable choice of variable.
Common exam mistake
Report reaction time in seconds; a larger ruler-drop distance means a slower response.
GCSE examination practice
Answer each question in full before opening the model answer. Check your work against the marking points and look for scientific key words.
Question 2 (3 marks)
Calculation
A ruler falls 0.20 m. Estimate reaction time using t = √(2d/9.81).
Show model answer / marking points
t = √(0.40/9.81) (1) = 0.202 s, about 0.20 s (2).
Question 3 (2 marks)
Evaluation
Why use several drops for each participant?
Show model answer / marking points
Repeat results reduce the effect of random variation (1) and allow a mean to be calculated (1).
Question 4 (2 marks)
Evaluation
Suggest one improvement to make the investigation more reliable and explain why it helps.
Show model answer / marking points
Repeat measurements and calculate a mean (1), reducing the influence of random variation/anomalies (1). Alternative valid improvement specific to the experiment with explanation can gain both marks.
This page was updated on: 12th June 2026