GCSE Physics revision

Stopping distance

Forces and braking

AQA 4.5.6.3.1

Your specification

AQA student objectives

Learning pathway

ALL 🎯

Estimate how the emergency stopping distance of a vehicle varies with speed.

MOST 🎯🎯

Interpret stopping-distance graphs to explain how stopping distance changes with vehicle speed.

SOME 🎯🎯🎯

Analyse how speed and other relevant factors affect stopping distance in an unfamiliar situation.

Revision summary

Read on screen, then print for Cornell-style active revision.

Thinking distance is the distance a car travels during the driver's reaction time, before the brakes are applied.
Reaction time is the time it takes for a driver to respond to a danger and apply the brakes.
Distance can be calculated using the equation s = vt, where s is distance, v is speed, and t is time.
If reaction time stays the same but speed doubles, the thinking distance also doubles.

1. Thinking Distance ExplainedAQA

Thinking distance is the distance a car travels during the driver's reaction time, before the brakes are applied.
Reaction time is the time it takes for a driver to respond to a danger and apply the brakes.
Distance can be calculated using the equation s = vt, where s is distance, v is speed, and t is time.
If reaction time stays the same but speed doubles, the thinking distance also doubles.

Braking distance is the distance a car travels after the brakes are applied until it comes to a complete stop.
A faster car has more speed to lose, so it takes longer to decelerate and travels further before stopping.
Even if two cars have the same braking force and deceleration, the faster car will have a greater braking distance.
The braking distance for a car travelling at double the speed more than doubles — it increases by a greater factor than thinking distance.

2. Braking Distance ExplainedAQA

Braking distance is the distance a car travels after the brakes are applied until it comes to a complete stop.
A faster car has more speed to lose, so it takes longer to decelerate and travels further before stopping.
Even if two cars have the same braking force and deceleration, the faster car will have a greater braking distance.
The braking distance for a car travelling at double the speed more than doubles — it increases by a greater factor than thinking distance.

Doubling the speed doubles the thinking distance, but more than doubles the braking distance.
This means the overall stopping distance increases significantly with even small increases in speed.
When estimating how stopping distance changes with speed, it is important to account for the non-linear increase in braking distance.

3. The Relationship Between Speed and Stopping DistanceAQA

Doubling the speed doubles the thinking distance, but more than doubles the braking distance.
This means the overall stopping distance increases significantly with even small increases in speed.
When estimating how stopping distance changes with speed, it is important to account for the non-linear increase in braking distance.

Speed limits are set based on how short stopping distances need to be in a given area.
The likelihood of sudden hazards, such as pedestrians or animals entering the road, is a key consideration.
The volume of traffic and the gap between vehicles affects whether a car can stop in time if the vehicle ahead brakes suddenly.
The number of junctions on a road influences how frequently drivers need to slow down or stop.
The presence of pedestrian crossings, such as zebra crossings or traffic lights, also affects the appropriate speed limit.

4. Factors Affecting Speed Limits on RoadsAQA

Speed limits are set based on how short stopping distances need to be in a given area.
The likelihood of sudden hazards, such as pedestrians or animals entering the road, is a key consideration.
The volume of traffic and the gap between vehicles affects whether a car can stop in time if the vehicle ahead brakes suddenly.
The number of junctions on a road influences how frequently drivers need to slow down or stop.
The presence of pedestrian crossings, such as zebra crossings or traffic lights, also affects the appropriate speed limit.

Higher speeds lead to longer stopping distances, increasing the risk of a driver being unable to stop in time to avoid a collision.
Roads in towns and cities in the UK typically have speed limits of 20, 30, or 40 mph, depending on the hazards present.
Motorways have higher speed limits because there are fewer sudden hazards such as pedestrians and junctions.

5. Why Speed Limits Matter for SafetyAQA

Higher speeds lead to longer stopping distances, increasing the risk of a driver being unable to stop in time to avoid a collision.
Roads in towns and cities in the UK typically have speed limits of 20, 30, or 40 mph, depending on the hazards present.
Motorways have higher speed limits because there are fewer sudden hazards such as pedestrians and junctions.

Use s = vt to calculate thinking distance, where v is the car's speed and t is the driver's reaction time.
In exam questions about stopping distance, always mention both thinking distance and braking distance separately.
When asked why a road has a particular speed limit, always refer to stopping distance in your answer.

6. Key Equations and Exam TipsAQA

Use s = vt to calculate thinking distance, where v is the car's speed and t is the driver's reaction time.
In exam questions about stopping distance, always mention both thinking distance and braking distance separately.
When asked why a road has a particular speed limit, always refer to stopping distance in your answer.