Effect of a factor on reaction time
GCSE Biology (8461) · Required practical 7 — method, variables, the marks examiners report students losing.
Plan and carry out an investigation into the effect of a factor (such as caffeine or practice) on human reaction time, using the ruler-drop test.
Apparatus
- A 30 cm ruler
- A chair and table so the person's arm rests with the hand over the edge
- A conversion table or the equation to turn drop distance into time
Method
- 1The person sits with their arm resting on the table and their hand over the edge, fingers open.
- 2Hold the ruler vertically so the 0 cm mark is between their thumb and finger.
- 3Without warning, drop the ruler; the person catches it as quickly as possible.
- 4Record the distance the ruler fell (the mark level with the top of the thumb).
- 5Repeat several times and take a mean; then change the factor being tested (e.g. after caffeine, or after practice) and repeat, keeping everything else the same.
Variables
Independent
The factor being tested (e.g. caffeine intake, or amount of practice)
Dependent
Reaction time (found from the ruler-drop distance)
Control
- Same person, same hand and same starting position
- Ruler dropped from the same point (0 cm between the fingers)
- No warning before each drop
Results & processing
- A shorter catch distance means a faster reaction time.
- Convert distance to time using a conversion table (or t = square root of (2d / g)); a smaller mean distance means a shorter reaction time.
- Compare the mean distance before and after the factor to judge its effect.
Where students lose marks
Warning the person before dropping the ruler.
Fix: Drop it without any signal, or they anticipate and the reaction time is not measured fairly.
Taking a single reading.
Fix: Repeat and take a mean to reduce the effect of anomalies and random error.
Changing more than one thing between trials.
Fix: Only change the factor under test; keep the person, hand and method the same.
Improve the method
- Use a computer/electronic reaction timer for a more precise and objective measurement.
- Repeat many times and take a mean, ignoring anomalies.
- Standardise the setup (same person, hand, seating) to make it a fair test.
Try it — exam-style
A student records catch distances of 18, 20 and 22 cm before caffeine, and 15, 16 and 17 cm after. Calculate both means and state what the results suggest.
Explain why the ruler-drop test is not measuring a reflex action.
Questions are written in the style of past AQA papers — never copied from them.
Drill it properly
Stuck on effect of a factor on reaction time?
Fair-test design and the maths of the mean are where marks are won here — I drill both, and your first lesson is free.