Stopping Distance

This lesson covers thinking distance, braking distance, the factors that affect each, and the relationship between speed and braking distance, as required by the Edexcel GCSE Combined Science specification (1SC0). Understanding stopping distance is vital for road safety questions in the exam.

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What Is Stopping Distance?

Stopping distance is the total distance a vehicle travels from the moment the driver sees a hazard to the moment the vehicle comes to a complete stop.

$\text{Stopping distance} = \text{Thinking distance} + \text{Braking distance}$Stopping distance=Thinking distance+Braking distance

graph LR
    A["Hazard seen"] -- "Thinking distance" --> B["Brakes applied"]
    B -- "Braking distance" --> C["Vehicle stops"]
    A -. "Stopping distance" .-> C

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Thinking Distance

Thinking distance is the distance the vehicle travels during the driver's reaction time — the time between seeing the hazard and pressing the brake pedal.

$\text{Thinking distance} = \text{speed} \times \text{reaction time}$Thinking distance=speed×reaction time

Typical Reaction Time

A typical human reaction time is 0.2 s to 0.9 s, with about 0.7 s as a commonly used value.

Worked Example

A car is travelling at 20 m/s. The driver's reaction time is 0.5 s. What is the thinking distance?