AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
The braking distance of a vehicle can be affected by adverse road and…
Full specification wording
Factors affecting braking distance 1: The braking distance of a vehicle can be affected by adverse road and weather conditions and poor condition of the vehicle.
The braking distance depends on the friction force available at the tyres and at the brakes.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 1 of 3
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The braking distance depends on the friction force available at the tyres and at the brakes. On a wet or icy road, a film of water or ice between tyre and surface lowers the friction, so the maximum braking force is smaller. Worn tyres with shallow tread cannot clear water, and worn brake pads or discs grip the wheel less firmly. In each case the same kinetic energy, ½ m v², has to be removed by a smaller force. Since work done = braking force × braking distance, a smaller force means the distance must be larger. Greater mass works the same way, because more kinetic energy has to be removed in the first place. Worn pads also overheat and fade sooner, so the braking force can fall further part way through a long stop.
What earns the marks
- Naming wet or icy road conditions as an adverse condition.
- Naming worn brakes or worn tyres as poor vehicle condition.
- Stating that the friction force between the tyres and the road is reduced.
- Linking the smaller braking force to the longer distance needed to remove the kinetic energy.
Common mistakes and how to put them right
Answering 'bad weather' alone, which the mark scheme ignores.
Saying ice makes the car heavier or the brakes colder.
Explaining a braking factor through the driver's thinking distance.
Claiming the brakes stop working altogether on an icy road.
Exam tips
- Build the chain: condition, then friction, then braking force, then distance.
- Use the words 'friction between the tyres and the road' rather than just 'grip'.
- If the question offers marks for an explanation, bring in work done = force × distance.
Try the lesson
The start of the Factors affecting braking distance 1: The braking distance of a vehicle can be affected by adverse road and weather conditions and poor condition of the vehicle. lesson, made from checked teaching notes for this specification point.
Have a go first
Which weather condition would increase the braking distance of a car?
Listen
The braking distance depends on the friction force available at the tyres and at the brakes. On a wet or icy road, a film of water or ice between tyre and surface lowers the friction, so the maximum braking force is smaller. Worn tyres with shallow tread cannot clear water, and worn brake pads or discs grip the wheel less firmly. In each case the same kinetic energy, ½ m v², has to be removed by a smaller force. Since work done = braking force × braking distance, a smaller force means the distance must be larger. Greater mass works the same way, because more kinetic energy has to be removed in the first place. Worn pads also overheat and fade sooner, so the braking force can fall further part way through a long stop. A strong answer earns marks for these points. naming wet or icy road conditions as an adverse condition. naming worn brakes or worn tyres as poor vehicle condition. stating that the friction force between the tyres and the road is reduced. linking the smaller braking force to the longer distance needed to remove the kinetic energy. Exam tip: Build the chain: condition, then friction, then braking force, then distance.
Key words
Say what each word means before you turn the card.
adverse conditions
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friction
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worn brakes and tyres
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work done
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See every definition
- adverse conditions
- Road and weather conditions that can affect the braking distance of a vehicle.
- friction
- The force available at the tyres and at the brakes, which is lowered by a film of water or ice between tyre and surface.
- worn brakes and tyres
- Poor vehicle condition in which worn tyres have shallow tread and worn brake pads or discs grip the wheel less firmly.
- work done
- Braking force multiplied by braking distance, so a smaller force means the distance must be larger.
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