Reaction time — AQA GCSE Physics
Test yourself on Reaction time with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Reaction time explained
Tiredness, alcohol, other drugs and distractions such as a phone all lengthen a driver's reaction time.
Read the full explanation
The mechanism is the same in each case: the brain takes longer to process the hazard and send the signal to the muscles, so more time passes before the brakes are applied. Since thinking distance = speed × reaction time, the thinking distance grows, and because stopping distance is thinking plus braking distance, the whole stop lengthens. The brakes, tyres and road are untouched, so the braking distance itself is unchanged. Data on alcohol shows two things worth quoting: the mean reaction time rises after drinking, and the increase is not the same for every person. A phone call or a conversation acts in exactly the same way, adding time before the driver's foot reaches the brake pedal.
Your focus
- Explain how a distraction lengthens the stopping distance by way of reaction time and thinking distance.
- Draw a conclusion about alcohol from a graph of individual reaction times, referring to both the mean and the spread.
- Sort a list of given factors into those that change thinking distance and those that change braking distance.
Reaction time exam tips
Marking Points
- one mark for naming a factor: tiredness, alcohol, another drug or a distraction
- one mark for stating that the reaction time increases
- one mark for linking that to a longer thinking distance
- one mark for concluding that the stopping distance increases
- one mark for a data conclusion such as the mean reaction time increases after alcohol but not by the same amount for everyone
Examiner Tips
- 💡Check whether the question asks about thinking or braking distance before you choose your factors.
- 💡When a graph of individual results is given, comment on the spread as well as the mean.
- 💡Say 'increases the reaction time' explicitly; naming the factor alone is usually only one of the marks.
Common Mistakes
- listing wet or icy roads, which lengthen the braking distance rather than the reaction time
- saying alcohol increases the braking distance
- writing that the driver is 'slower' without naming reaction time or thinking distance
- claiming every person's reaction time rises by the same amount after drinking, which the data does not support