Investigating Reaction Time
Practise Investigating Reaction Time for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. The required practical measures reaction time using the ruler-drop test, and how factors such as caffeine can affect it.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
This required practical investigates how a factor such as caffeine or practice affects human reaction time.
The standard method uses a falling ruler. One person holds a ruler vertically with zero between the partner's thumb and forefinger. Without warning they drop it, and the distance fallen before it is caught is recorded. A shorter distance means a faster reaction time.
Control variables matter here more than in most practicals, because human reactions are so variable. The same hand should be used each time, the ruler should be dropped from the same position, and there should be no warning or countdown. Repeating and taking a mean reduces the effect of random variation.
Revision notes
The method
One person holds a ruler vertically with the zero mark level with the top of the partner's thumb and forefinger.
Without warning they release it. The partner catches it as quickly as possible, and the distance on the ruler at the catch point is recorded. Repeat and calculate a mean.
Control variables
Use the same hand each time, hold the ruler at the same starting position, and give no warning or countdown.
The same person should drop the ruler throughout. Without these controls the differences measured could be caused by the method rather than the factor being tested.
Interpreting results
A shorter catch distance means a faster reaction time.
Repeats are essential because human reaction times vary considerably. Taking a mean reduces the effect of that random variation and makes any real difference clearer.
Key points
- A shorter catch distance means a faster reaction time.
- Use the same hand and starting position each time.
- Give no warning before dropping the ruler.
- Repeat and calculate a mean.
- Repeats reduce the effect of random variation.
- Caffeine is a common factor investigated.
Worked examples
Example 1
Explain why the ruler must be dropped without any warning. [2 marks]
Model answer
If the person knew when it was coming they could anticipate the drop (1 mark), so the measurement would not be a true reaction time (1 mark).
Example 2
Explain why the investigation should be repeated several times for each person. [2 marks]
Model answer
Human reaction times vary naturally between attempts (1 mark), so repeating and taking a mean reduces the effect of this random variation and gives a more reliable result (1 mark).
Example 3
A student catches the ruler at 18 cm on the first attempt and 12 cm on the fifth. Suggest what this shows. [2 marks]
Model answer
The shorter distance means a faster reaction time (1 mark), suggesting the student's reaction time has improved with practice (1 mark).
Common mistakes
Giving a countdown before dropping.
Any warning allows anticipation, so the measurement is not a true reaction time.
Using a different hand between trials.
This is a variable that must be controlled for a fair test.
Taking only one reading.
Human reaction times vary, so repeats and a mean are essential.
Saying a longer distance means a faster reaction.
The opposite — a shorter distance means the ruler was caught sooner.
Exam tips
- Name at least two control variables when describing the method.
- Explain repeats in terms of reducing random variation.
- Remember shorter distance means faster reaction.
- Mention that the same person should drop the ruler throughout.
Key terms
- Reaction time
- The time taken to respond to a stimulus.
- Control variable
- A variable kept the same to ensure a fair test.
- Mean
- The average of repeated measurements.
- Random variation
- Natural variability between repeated measurements.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.