RP7: Required practical activity 7: Reaction time
Not started yet — this one needs some love.
Aim: plan and carry out an investigation into the effect of a factor on human reaction time using the ruler drop test.
Independent variable: the factor being investigated — the standard method investigates the effect of practice (attempt number). Other valid factors include distraction or caffeine (with appropriate ethical precautions).
Dependent variable: distance the ruler falls (cm) before the catcher grips it, converted to reaction time (seconds) using a conversion table. The mean of several trials is used.
Control variables:
same ruler
same hand throughout (weaker hand)
same starting position (forearm resting on table, hand overhanging the edge)
same person dropping the ruler
ruler dropped without warning each time
same rest period between attempts
Method
The catcher sits at a table with their weaker arm resting on the table and their hand overhanging the edge.
The dropper holds a metre ruler vertically with the 0 cm end between the catcher's thumb and index finger.
The catcher spreads their fingers slightly — ready but not touching the ruler.
The dropper positions the ruler so the 0 cm mark is level with the top of the catcher's thumb, then drops it without warning or countdown.
The catcher grips the ruler as quickly as possible. Read off and record the distance at the level of the top of the thumb (cm).
Repeat at least 10 times. Allow a short rest between attempts.
Use the conversion table to convert each distance into a reaction time (s).
Calculate the mean reaction time for early attempts versus later attempts to see whether practice reduces reaction time.
Swap roles. Plot a graph of reaction time (s) on the y-axis against attempt number on the x-axis.
Safety
Falling ruler — risk of injury if the ruler is grabbed too hard or the catcher misses; grip only the ruler and keep fingers clear of the desk edge; stop immediately if any discomfort occurs.
Informed consent — all participants must agree to take part and may withdraw at any time; stop immediately if a participant feels unwell or uncomfortable.
Caffeine or other substances — if testing the effect of a substance, do not use doses that could cause harm; obtain teacher and parental consent in advance; exclude participants with relevant health conditions.
Common exam mistakes
In the ruler-drop test, the catcher must not know exactly when the ruler will be released; otherwise prediction is being tested instead of reaction time.
Control the starting position, same hand, same ruler, same dropper/instructions and rest time. A fair test changes only the chosen independent variable.
Reaction time varies naturally, so repeats and a mean are needed; ignore anomalies only with a clear reason.
If testing caffeine or exercise, include sensible safety/ethics such as consent and avoiding unsafe doses or unwell participants.