Reaction Time
Get to grips with Reaction Time for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Reaction time is typically between 0.2 and 0.9 s and is increased by tiredness, alcohol and distractions.
Free downloads
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
Reaction time is the time between a person perceiving a hazard and beginning to respond. Typical values for a driver are between 0.2 and 0.9 seconds, and reaction times vary from person to person.
Several factors increase reaction time. Tiredness, distractions such as a mobile phone, drugs including some prescribed medicines, and alcohol all lengthen it. A longer reaction time means a greater thinking distance at any given speed.
Reaction time is commonly measured with the ruler drop test. A ruler is dropped without warning between the thumb and finger, and the distance it falls before being caught is converted into a time. Because human reaction times vary between attempts, repeats and a mean are essential.
Revision notes
Typical values and variation
Reaction time is the time between perceiving a hazard and beginning to respond.
Typical driver values are 0.2 to 0.9 seconds. They vary between individuals, and for the same individual on different occasions.
Factors that increase it
Tiredness, distractions such as using a mobile phone, drugs including some prescribed medicines, and alcohol.
Each lengthens the reaction time, which increases the thinking distance and therefore the total stopping distance at any given speed.
Measuring reaction time
The ruler drop test: a ruler is dropped without warning between the thumb and finger, and the catch distance is recorded.
A shorter distance means a faster reaction. Repeat and take a mean, because human reaction times vary considerably between attempts.
Key points
- Reaction time is typically 0.2 to 0.9 seconds.
- Reaction times vary between people.
- Tiredness and distractions increase reaction time.
- Drugs and alcohol increase reaction time.
- A longer reaction time increases thinking distance.
- The ruler drop test measures reaction time.
Worked examples
Example 1
Give three factors that can increase a driver's reaction time. [3 marks]
Model answer
Tiredness (1 mark). Distractions such as using a mobile phone (1 mark). Drugs or alcohol (1 mark).
Example 2
A driver travels at 20 m/s with a reaction time of 0.7 s. Calculate the thinking distance. [2 marks]
Model answer
Thinking distance = speed × reaction time = 20 × 0.7 (1 mark) = 14 m (1 mark).
Example 3
Explain why the ruler drop test should be repeated several times. [2 marks]
Model answer
Human reaction times vary between attempts (1 mark), so repeating and taking a mean reduces the effect of this variation and gives a more reliable result (1 mark).
Common mistakes
Giving a reaction time in minutes.
Typical values are fractions of a second, from 0.2 to 0.9 s.
Saying reaction time affects braking distance.
It affects thinking distance; braking distance depends on speed and braking force.
Taking a single ruler drop reading.
Repeats and a mean are needed because reaction times vary.
Saying only alcohol affects reaction time.
Tiredness, distractions and drugs also lengthen it.
Exam tips
- Learn the 0.2 to 0.9 second range.
- Link reaction time specifically to thinking distance.
- Give several factors when asked.
- Explain repeats in terms of natural variation.
Key terms
- Reaction time
- The time between perceiving a hazard and responding.
- Thinking distance
- Speed multiplied by reaction time.
- Ruler drop test
- A method of measuring reaction time.
- Mean
- The average of repeated measurements.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.