# What factors affect the stopping distance of a car?

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Introduction

Richard Lai Physics 01/05/2007

4th Form FI MATH

Sc1- What factors affect the stopping distance of a car?

Prediction

1.) Speed

My prediction is that the more speed the car is travelling with, the longer the stopping distance will be after applying the brake.

The velocity of the car is related to the kinetic energy of the car. The equation for finding the kinetic energy is = 1/2 × mass × velocity2. To remove the kinetic energy of the car wheels, i.e. applying the brakes on, the brakes do work, which can be calculated with the equation W=Force × distance (m). In order to stop the car completely, the brakes have to convert all the kinetic energy to heat energy, sound energy and other kinds of energy. According to the Principal of Conservation of Energy, energy can be changed from one form to another, but it cannot be created nor destroyed. In this case,

Kinetic Energy (of car) = Work done (by brakes)

1/2mv2 = Fd

Using this balanced equation, we can find out if my prediction is right. Here we take away any constant terms, which are ‘1/2’, mass and force, which leaves ‘v2’ and ‘d’, making the equation:

v2 = d

v2 α d

This is exactly what I am predicting –the velocity2 is proportional to the stopping distance.

2.) Braking Force

My prediction is that the more braking force applied on the wheels, the shorter the stopping distance is.

Middle

Starting Position

Stopping Distance (m)

Average Velocity (m/s)

v2

1st Try

2nd Try

3rd Try

1

0.82

0.833

0.802

0.818

0.669

2

0.992

0.991

1.02

1.001

1.002

3

1.11

1.07

1.11

1.097

1.203

4

1.27

1.24

1.27

1.26

1.588

5

1.33

1.32

1.35

1.33

1.769

6

1.50

1.53

1.50

1.51

2.280

7

1.64

1.69

1.70

1.677

2.812

8

1.81

1.77

1.70

1.76

3.098

9

1.85

1.84

1.78

1.823

3.323

10

1.92

1.93

1.89

1.913

3.650

Results for the Change of Stopping Distance affected by the Speed

Starting Position | Stopping Distance (m) | Average Stopping | ||

1st Try | 2nd Try | 3rd Try | Distance (m) | |

1 | 0.48 | 0.48 | 0.48 | 0.48 |

2 | 0.65 | 0.65 | 0.69 | 0.66 |

3 | 0.84 | 0.82 | 0.84 | 0.83 |

4 | 1.10 | 1.16 | 1.12 | 1.13 |

5 | 1.37 | 1.40 | 1.38 | 1.38 |

6 | 1.61 | 1.63 | 1.63 | 1.62 |

7 | 1.89 | 1.84 | 1.82 | 1.85 |

8 | 2.14 | 2.06 | 2.13 | 2.11 |

9 | 2.32 | 2.28 | 2.26 | 2.29 |

10 | 2.59 | 2.54 | 2.57 | 2.57 |

Conclusion

Sufficiency of Results

I have 10 results for each experiment, which is enough to make my graph clear, so having 10 results is plenty, but, of course, more would be good as they make the graph more reliable.

Further Work

Additional relevant evidence can be found with some further work. This is to be done with a totally different experiment, but should be much more better.

For the speed, we can use a car being driven on a road built with the same material (tarmac) staying flat all the way through so that the road surface would be the same all the way down. The braking force would always be the same if we press the brake footpad all the way down, so it is constant. The speed can be read inside the car, so when it reaches to the right speed, the driver can then brake the car, and the stopping distance can be measured from the tyre skid mark (therefore the car has to be fairly fast). This will be quite dangerous and requires a large amount of space (only if we can use the whole of M1…).

As for the braking force, I honestly don’t have any ideas apart from using a trolley, as it is very complicated (or impossible) to control the braking force of a vehicle, unless they can be digitally controlled, then we can do this experiment on a flat road by increasing the braking force with a constant speed all the way through the experiment.

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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