# Investigating the relationship between the speed of a model car and its stopping distance.

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Introduction

Matthew Richards 5L Mr Moncaster

Investigating the relationship between the speed of a model car and its stopping distance

Introduction

I am going to investigate the stopping distance of a model car against its speed. To investigate this relationship I will be rolling a model car down a ramp, set at different heights, measuring the speed and stopping distance for each run then averaging these results.

Predictions

The faster the model car is travelling the greater the stopping distance of the car will be.

The main reason for this is friction, there are other factors, such as air resistance, but it is very difficult for us to measure this on such a small scale so we will dismiss the possibility of the car being slowed down by this factor. Friction is the force that opposes the motion between two surfaces in contact with another.

You may be wondering how I have come about this prediction, well using scientific knowledge and my general knowledge this is the conclusion I have come to. I think it is best if I use an example to explain; taking a real car as this example, the Highway Code gives us the typical stopping distances of a car travelling at significant speeds (i.e. 20mph, 30mph, 40mph etc):

20mph 12m

30mph 23m

40mph 36m

50mph 53m

60mph 73m

70mph 96m

(This is not to scale)

This diagram includes the thinking distance of the driver car but as a human is not driving my model car this can be removed and we are left with this raw data:

Speed (mph) | Stopping Distance (m) | Speed2 |

20 | 6 | 400 |

30 | 14 | 900 |

40 | 24 | 1600 |

50 | 38 | 2500 |

60 | 55 | 3600 |

70 | 75 | 4900 |

(I have put speed2 on in an extra column for another prediction that I will make and explain later on in the coursework.)

Middle

In total I have 10 blocks each of equal height, which gives me 10 different heights to release the car from. At each of these heights I will take 3 different readings. Each height will have 6 readings in total, the 3 different speeds and the 3 different stopping distances, it is possible for us to workout the average speed and distance for each height thus giving us an average speed and distance for each height. My simple results table would, therefore look

something like this:

(Remember 1 block is 1 cm high)

Height | Speed | Distance |

1 Block | 0.52m/s | 25 cm |

1 Block | 0.49 m/s | 24 cm |

1 Block | 0.51 m/s | 23 cm |

Average | 0.51 m/s | 24 cm |

2 Blocks | 0.68 m/s | 41 cm |

2 Blocks | 0.70 m/s | 42 cm |

2 Blocks | 10.2 m/s | 39 cm |

Average | 0.69 m/s | 40.7 cm |

A Fair Test?

There are a few variables in this test that need to be controlled / kept the same, we need to use the same:

- Car, (this means there will be the same amount of friction acting on the desk each time as every car would have different amounts of friction acting on it as it moves.
- Work Surface / Desk, (this is varnished wood, with dents and holes in its surface)
- Light Gate,
- Electronic Timer
- Ramp,
- Blocks.

If we were to change any of these then we would make the test unfair.

Safety

There are few dangers in this experiment, the only real danger that I can foresee is the main electricity that is used to power the light gate and electronic timer but the room is fitted with a RCD that would isolate the circuit in the room if anything was to go wrong, thus making the room safe. We also need to ensure that all

Conclusion

My evidence supports my conclusion, that as the speed increases so does the stopping distance of the model car and that the stopping distance is proportional to the velocity squared.

Further Work

Apart from the obvious thing we could do, that is to take more readings to a higher degree of accuracy there are other things that we could investigate in the experiment, such as adding more predictions to prove / disprove. We could also do the experiment on a much larger scale with real cars to take an example or we could increase the weight of the car for each different set of runs; this would work by running a car of say 50g down the run at 2 blocks high then running a car of say 100g down the same ramp again at 2 blocks high. This would give us more data to work from and would allow us to create more detailed predictions such as:

As the mass of the car increases so do the stopping distances.

Again we could look at the relationship between the two results and I would be able to gather and form more complicated results from them.

Summary

I have found out all the data I have said I will found out in my plan and I have noticed, investigated and described certain patterns and predictions that I have made. I have processed my own results and I have been able to draw conclusions from them and to notice any trends / patterns that have formed, I have also noticed anomalies and any stray data in my results and I have pointed these out and talked about them and the reasons that I have them.

Over-all I think this has been successful project for me and I have learnt much about the relationships between stopping distances of the car and it’s speed.

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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