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# Physics Coursework - car braking investigation.

Extracts from this document...

Introduction

Barbara Palvin

Centre devised assessment

P2 Topic 9 As Fast as You Can

Introduction

The stopping distance is the distance taken for the car to stop. It includes the distance that is travelled during the thinking time of the driver, (registering the need to stop, then moving the foot to the break pedal.) It also includes the braking distance; the distance travelled after the break is applied. The thinking distance will vary from person to person, as the braking distance will vary between cars. However, and average can be made. The overall stopping distance is calculated by adding together the thinking distance and the braking distance.

Analysis

 Speed (mph) Thinking Distance (m) Braking Distance (m) Overall stopping distance (m) 20 6 6 12 30 9 14 23 40 12 24 36 50 15 38 53 60 18 55 73 70 21 75 96

The graph shows a positive correlation in braking and thinking distances.

Middle

Stopping distance can be affected by many factors, the main ones being the speed the car is travelling at, the use of a mobile phone, drink-driving and wet weather.

• The thinking distance is always the same, no matter what speed the car is travelling at. But because more distance is covered over the same period of time when driving fast, the driver has less time to react to any hazards. Also, a small increase in speed will increase the braking distance: if the speed is double, the braking distance will be increased by four times.
• Using a hand-held mobile phone diverts much of the driver’s attention from the road, and so the thinking distance is increased greatly when using one.
• Alcohol and illegal drugs cause thinking time to be increased, because it takes the driver longer to process information. A drunk driver may also not press as hard on the brake as a sober driver. The extra time it takes the driver to press the brake, means that the car would be travelling at a faster speed when it hits the pedestrian, causing a more serious injury.
• When roads are wet, the car has less grip on the road surface, resulting in more skids and increased braking distances. Thinking distance can also be increased by reduced visibility due to rain. Also, if the tread depth of the tyres is low, the rubber has less grip on the road, and this is even more dangerous when driving in bad weather conditions.

Stopping distance = thinking distance + braking distance

Thinking distance = speed x reaction time                s=d/t

Thinking distance is affected by:

• Tiredness
• Alcohol
• Drugs
• Distractions

Tiredness, alcohol and drugs all make the mind think slower and take longer to process information

Braking distance is affected by:

• Speed
• Weight of the car
• Braking efficiency

Conclusion

Mass x velocity = momentum

A bigger vehicle (e.g. 4x4) will have a bigger stopping distance because it gains more momentum through kinetic energy, and so the driver may well have the same reaction time as a car driver (Mini), the braking distance will be increased, therefore taking longer to stop.

The only reason why stopping distances should not have been published, is because it could encourage some drivers to try and disprove the data. Although this would be a very irresponsible thing to do, there are some people, usually teenagers, who would risk such dangerous actions.

However, many people are more vigilant when driving faster, e.g. on motorways, than when driving on A roads:

We can see that there are more serious injuries and deaths by drunk drivers on urban and rural roads than motorways. This is likely to be because when driving on a motorway, people tend to take more care and are more sensible.

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

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