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P5 U) Braking Distance
P5 U) Braking Distance
The drivers of cars, bikes, lorries and any other vehicle may have to perform an emergency stop. An emergency stop is where the driver has to apply the full braking force to stop a vehicle in the shortest possible distance to prevent the vehicle from hitting a hazard/ emergency in front of them. The stopping distance of a vehicle is the distance covered between a driver noticing a hazard and the vehicle becoming stationary. The stopping distance is the sum of the thinking distance and the braking distance.
The thinking distance is the distance travelled during the driver’s reaction time, and the braking distance is the distance travelled whilst the brakes are applied.
Thinking Distance
Thinking distance is the distance travelled during the driver’s reaction time (it is the distance travelled between the driver noticing the hazard and applying the brakes). The thinking distance is affected by two major factors:
Thinking distance is the distance travelled during the driver’s reaction time (it is the distance travelled between the driver noticing the hazard and applying the brakes). The thinking distance is affected by two major factors:
- Speed of the vehicle. The faster the vehicle is travelling, the greater the thinking distance. For example, let’s suppose that my reaction time was 0.5 seconds. If I was travelling at 10 m/s, my thinking distance would be 5 metres. However, if I was travelling twice as fast (20 m/s) and my reaction time was the same, my thinking distance would be twice as long (10 metres).
- Reaction time. The faster the reaction time, the shorter the thinking distance. The reaction time of individuals can be affected by how tired the driver is and whether they have taken any substances (caffeine, drugs or alcohol; caffeine would decrease reaction time, which would decrease the thinking distance. Drugs and alcohol will increase reaction time, which would increase the thinking distance).
Braking Distance
The braking distance is the distance travelled whilst the brakes are on. It is affected by 3 factors:
The braking distance is the distance travelled whilst the brakes are on. It is affected by 3 factors:
- Speed of the vehicle. The faster a vehicle is travelling, the greater the braking distance.
- The quality of the brakes. The brakes on a car need to be maintained to ensure their performance. Worn out or old brakes will apply a lower braking force, which will increase the braking distance. Brakes on newer cars are generally able to apply a greater braking force than the brakes on older cars, which results in newer cars having a shorter braking distance (for the same speed).
- The level of grip. This is dependent on 3 factors:
- The road surface. A more grippy road will provide greater friction between the types and the road, which means that the braking distance will be shorter. If the road has less grip, there will be less friction between the tyres and road, which results in a greater braking distance; for example, the braking distance would be greater on a gravel road compared to a tarmac road for the same speed.
- The level of tyre tread. Road authorities across the world place requirements on the tread depth of tyres for vehicles so that the tyres can deal with different road conditions and weathers. If tyre tread is too low, there is a greater chance of the vehicle skidding when it is braking and this increases the braking distance as well as potentially causing the driver to lose control of the vehicle.
- Weather conditions. Wet, icy and snowy roads have less grip than the same road in dry conditions. This means that the braking distance is longer for roads in wet, icy and snowy conditions.