Required practical: reaction timeSpec 4.5.2.1
In short
Reaction time is the time taken to respond to a stimulus. In this required practical, a partner drops a ruler without warning and the volunteer catches it as fast as possible: a shorter distance fallen means a faster reaction. You change one factor, such as caffeine or practice, keep the other variables the same, and repeat to calculate a mean.
Required practical activity 7 (activity 6 in Combined Science): plan and carry out an investigation into the effect of a factor on human reaction time.
Reaction time is the time taken to respond to a stimulus. A common method uses a ruler.
- The volunteer sits with their forearm resting on the edge of a table and their hand over the edge.
- A partner holds a ruler vertically so that the zero mark is level with the volunteer’s thumb and finger, which are about to grip it.
- Without warning, the partner drops the ruler.
- The volunteer catches it as fast as possible. Read the distance on the ruler at the top of their thumb.
- Repeat several times and calculate a mean for each condition.
- Independent variable: the factor you change, for example caffeine, a distraction, practice or which hand is used.
- Dependent variable: reaction time, shown by the distance the ruler falls (a shorter distance means a faster reaction), or by a time from a computer test.
- Control variables: the same volunteer, the same hand, the same ruler, the same drop height, and the same method of reading the result.
- Safety: the risk is low. Make sure nobody is pressured into taking a drink or doing anything they are not comfortable with.
Repeating the test and taking a mean makes the results more reliable. Ignore any anomalous result when you calculate the mean.
From numbers to a graph
A student measured reaction time (in s) five times: 0.31, 0.29, 0.33, 0.30, 0.32. Calculate the mean, then say how the means for two conditions would be shown on a bar chart.
- Add the five results: 0.31 + 0.29 + 0.33 + 0.30 + 0.32 = 1.55
- Divide by the number of results: 1.55 ÷ 5 = 0.31
- Draw one bar per condition, labelled on the x-axis, with bar height equal to the mean reaction time on the y-axis (in s).
Answer: Mean reaction time = 0.31 s.
You may be asked to turn a table of reaction times into a graph, or read values from a graph into a table. Label axes with the quantity and unit, for example ‘Reaction time (s)’. Use a bar chart when one variable is a category.
Quick check
What is the CNS?
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The central nervous system: the brain and spinal cord.
Put these in order: motor neurone, sensory neurone, relay neurone.
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Sensory neurone, relay neurone, motor neurone.
Why are reflex actions important?
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They are automatic and rapid, protecting the body from harm without involving the conscious part of the brain.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026