Edexcel iGCSE Physics -1.19–1.20 Stopping Distance and Factors Affecting It- Study Notes- New Syllabus
Edexcel iGCSE Physics -1.19–1.20 Stopping Distance and Factors Affecting It- Study Notes- New syllabus
Edexcel iGCSE Physics -1.19–1.20 Stopping Distance and Factors Affecting It- Study Notes -Edexcel iGCSE Physics – per latest Syllabus.
Key Concepts:
1.19 know that the stopping distance of a vehicle is made up of the sum of the thinking distance and the braking distance
1.20 describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time
Stopping Distance of a Vehicle
The stopping distance of a vehicle is the total distance travelled from the moment a driver notices a hazard to the moment the vehicle comes to a complete stop.
Stopping distance is important for road safety because it determines how much space a vehicle needs to stop safely.
Components of Stopping Distance
The stopping distance is made up of two parts:
- Thinking distance
- Braking distance
Thinking Distance
Thinking distance is the distance travelled while the driver is reacting to a hazard before the brakes are applied.
- Depends on the driver’s reaction time.
- Increases with speed.
- Affected by tiredness, alcohol, drugs, and distractions.
Formula for thinking distance:
\( \mathrm{thinking\ distance = speed \times reaction\ time} \)
Braking Distance
Braking distance is the distance travelled after the brakes are applied until the vehicle stops.
- Depends on the vehicle’s speed.
- Affected by road conditions, tyre condition, and braking force.
- Increases rapidly with speed.
Key Relationship
The relationship between stopping distance, thinking distance and braking distance is:
\( \mathrm{stopping\ distance = thinking\ distance + braking\ distance} \)
Understanding the Relationship
- Even with good brakes, stopping distance can be large due to thinking distance.
- Higher speed increases both thinking and braking distances.
- Poor conditions mainly increase braking distance.
Key Idea
- Stopping distance is not just braking distance.
- Driver reaction time is always involved.
- Reducing speed greatly reduces stopping distance.
Important Points to Remember
- Stopping distance is measured in metres (m).
- Thinking distance depends on the driver.
- Braking distance depends on the vehicle and road.
Example
A car has a thinking distance of \( \mathrm{12\ m} \) and a braking distance of \( \mathrm{28\ m} \). Calculate the stopping distance.
▶️ Answer / Explanation
Use: \( \mathrm{stopping\ distance = thinking\ distance + braking\ distance} \)
\( \mathrm{stopping\ distance = 12 + 28} \)
\( \mathrm{stopping\ distance = 40\ m} \)
Example
A driver is travelling at \( \mathrm{20\ m/s} \) and has a reaction time of \( \mathrm{0.8\ s} \). Calculate the thinking distance.
▶️ Answer / Explanation
Use: \( \mathrm{thinking\ distance = speed \times reaction\ time} \)
\( \mathrm{thinking\ distance = 20 \times 0.8} \)
\( \mathrm{thinking\ distance = 16\ m} \)
Factors Affecting Vehicle Stopping Distance
The stopping distance of a vehicle is the total distance travelled from when a driver first notices a hazard to when the vehicle comes to a complete stop.
Stopping distance depends on both the driver and the vehicle, as well as external conditions such as the road surface.
Key Relationship
The stopping distance is given by:
\( \mathrm{stopping\ distance = thinking\ distance + braking\ distance} \)
Main Factors Affecting Stopping Distance
The main factors are:
- Speed of the vehicle
- Reaction time of the driver
- Mass of the vehicle
- Road conditions
1. Speed
Speed has the greatest effect on stopping distance.
- Higher speed increases thinking distance.
- Higher speed also increases braking distance.
- Braking distance increases rapidly as speed increases.
Doubling the speed more than doubles the stopping distance.
2. Reaction Time
Reaction time affects only the thinking distance.
Thinking distance formula:
\( \mathrm{thinking\ distance = speed \times reaction\ time} \)
- Longer reaction time increases stopping distance.
- Reaction time increases due to tiredness, alcohol, drugs, and distractions.
3. Mass of the Vehicle
The mass of a vehicle mainly affects the braking distance.
- A larger mass means more momentum.
- More force is required to stop the vehicle.
- This results in a longer braking distance.
Heavy vehicles such as trucks take longer distances to stop.
4. Road Conditions
Road conditions affect the amount of friction between the tyres and the road.
- Wet or icy roads reduce friction.
- Reduced friction increases braking distance.
- Loose surfaces (gravel) also reduce grip.
Good road conditions provide more friction and shorter braking distances.
Key Idea
- Stopping distance depends on both thinking and braking distances.
- Some factors affect the driver, others affect the vehicle.
- Reducing speed greatly reduces stopping distance.
Important Points to Remember
- Reaction time affects only thinking distance.
- Road and vehicle factors mainly affect braking distance.
- Stopping distance is always measured in metres (m).
Example
A driver increases speed from \( \mathrm{15\ m/s} \) to \( \mathrm{25\ m/s} \). State two reasons why the stopping distance increases.
▶️ Answer / Explanation
Thinking distance increases because the car travels further during the reaction time.
Braking distance increases because the car has more kinetic energy to lose.
Example
A car is travelling on an icy road. Explain why its stopping distance is longer than on a dry road.
▶️ Answer / Explanation
The icy road reduces friction between the tyres and the road.
Reduced friction increases braking distance, so the total stopping distance is larger.