# 5.8.4 Factors Affecting Thinking Distance & Reaction Time

### Factors Affecting Reaction Time

• Human reaction time can depend on a number of factors. It is increased by:
• Tiredness
• Distractions (e.g. using a mobile phone)
• Intoxication (i.e. consumption of alcohol or drugs)
• Since these factors can affect the reaction time of a human, they directly affect the thinking distance when travelling in a car
• The main factor that affects the thinking distance is the car’s speed
• Additional factors, like those given above, can affect the thinking distance

#### Worked Example

The graph below shows how the thinking distance of a driver depends on the speed of the car.

(a) Describe the connection between thinking distance and speed.

(b) Some people drive when they are tired, despite warnings against doing so. Draw a new line on the graph to show how thinking distance varies with speed for a tired driver.

Part (a)

Step 1: Check if the line is straight and if it goes through the origin

• The graph shows a straight line through the origin
• Therefore, the thinking distance is directly proportional to the speed of the car

Part (b)

Step 1: Recall the factors which affect the thinking distance

• Three additional factors affect the thinking distance, because they affect human reaction time:
• Tiredness
• Distractions
• Intoxication
• Hence, a tired driver’s reaction time is greater (i.e. it takes longer for them to react)

Step 2: Draw a line that shows greater thinking distance for the same speed

• At the same speed, a tired driver’s thinking distance will be greater than a driver who is alert
• This means a line should be drawn with a steeper gradient, as shown below:

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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