Identify the factors affecting the braking distance of a toy car.

Oliver Heywood Physics Coursework 02/05/2007

Planning the Investigation

Aim:

My aim through this experiment is to identify the factors affecting the braking distance of a toy car; the factor I am investigating is Speed. The reason I choose speed to investigate was because I thought of all the possible outcomes and worked out that the mass would only be able to go up to no more than five masses on the car as there would not be enough carpet as a breaking area without falling off the table. So from the results I can plot graphs of Speed and Breaking Distance against the mass of the car. I am investigating the speed variable and looking at the breaking distance.

Method:

To begin with a car which is 2.5 inches long and weighs 52.2g is placed at a height on the plastic runway. The car runs down the track and onto a piece of carpet. I then take the results that come up on the computer screen, which is the speed, measured in m/s. These results are recorded by a light gate sensor; the car travels down the runway and intercepts the beam of the light gate. The speed is recorded by the car going through the light gate with its front end and then when the back end of the car has gone through, it measures how long it took the whole car to pass through the light gate. The speed is sent through the control box and into the computer showing the wide-ranging results on the screen.

I must remember that the release of the car from my hand, which starts the car rolling, will be of a force but not a noticeable force as the car gets all of its acceleration from the height and steepness of the track at the various heights. Down the track acceleration operates on the car until the car hits the carpet runway where the braking acts with a friction force until it comes to a stop, giving off a small amount of heat and sound energy. In the real experiment I release the car from the top then gradually come to the bottom of the ramp. The decrease in height on the ramp is a cars length every time. For the real investigation I will be taking and using 32 results plotting them into a results table including the preliminary results.

There are precautions I must take in the investigation that are I must never change the car because it may have a different mass affecting the speed or breaking distance. Use the same ramp as it run differently affecting the factors. I must always do the each experiment twice so I make it a fair test and to make sure that the results are not being recorded wrongly. So I can then with two results work out the Average speed and breaking results.

The apparatus and measuring equipment I am going to be using is listed below; all of these are used at sometime in the experiment:

Hot Wheels Set (track and Cars)

Masses - can be attached to the cars (10g each mass)

Light gate, Sense and Control apparatus and PC Software

Metre rulers (cm)

Stop Clocks (seconds)

Carpet strip (breaking area)

Below you can see a diagram of the apparatus set up:

First of all I am going to make a results table containing two speeds then an average ...

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The apparatus and measuring equipment I am going to be using is listed below; all of these are used at sometime in the experiment:

Hot Wheels Set (track and Cars)

Masses - can be attached to the cars (10g each mass)

Light gate, Sense and Control apparatus and PC Software

Metre rulers (cm)

Stop Clocks (seconds)

Carpet strip (breaking area)

Below you can see a diagram of the apparatus set up:

First of all I am going to make a results table containing two speeds then an average speed. I will also measure the braking distance of the vehicle, which is the distance from the end of the ramp to the end of the car. We do this for each speed then take both breaking distances and average them to make an average breaking distance, measured in centimetres. These preliminary results can be seen in a table below: My results I know are not of a wide range as the speed only varies from 1.76 to 2.24. These results can just give you an idea as my real results have a lot bigger range.

The preliminary results as you can see only have a small range of results so the average speed and the average breaking distance both have a pattern of results, which is very small. But the results of the main experiment are a lot different as you can see I have a very wide range in both areas of speed and breaking distance. These can be seen below:

These results compared to the preliminary ones can give you a real look what the experiment was like as I can now plot graphs using the speed and breaking distances against one and other. The range is a lot bigger in the speed and in the breaking distance too.

Analysis

As the speed increases so does the average breaking distance this maybe a directly proportional relationship this means when the speed doubles so does the breaking distance.

Speed at an average breaking distance of 40cm is 1.12 m/s
Speed at an average breaking distance of 80cm is 1.8m/s
1.8 / 1.12 = 1.61

Speed at an average breaking distance of 50cm is 1.4m/s
Speed at an average breaking distance of 100cm is 2.3m/s
2.3 / 1.4 = 1.64

If the relationship was directly proportional then the answers I should have received would have been 2. In fact the breaking distance when the speed is doubled is only multiplied by about 1.6. This does not rule out the possibility of the relationship directly proportional but it does not prove this theory either.

The Physics of the investigation

The physics of the investigation lies in the experiment. I release the car from the top of the runway which runs down the ramp picking up speed getting to its greatest velocity. Upon hitting the carpet runway forces quickly act upon the car. There is resistance with a drag motion pulling the car backward to a stop, and a huge amount of friction acts upon the car giving off a small amount of heat and sound. You can show the amount of friction by releasing the car at varied heights and measuring the breaking distance. For all the energy present in this investigation you can use the equation Gravitational Potential Energy Kinetic Energy (GPE KE).

Relevant Variables means things you can change in your experiment. The relevant variables for my experiment affecting Speed are listed below:

The height of the plastic slope, the steepness which can be changed by either using a different ramp of different sizes bigger or smaller. Or simply moving the car up and down the ramp and releasing at different points. This variable not only affects speed but mass and breaking distance also.
You can change the mass of a vehicle by adding or removing weights. My car which was a miniature white 355 Ferrari weighed in at 52.2g.

By adding on masses this would hopefully alter the breaking distance and the speed. So a theory to this would be if I was to add mass to the car surely the speed and the breaking distance would increase. To support this I would have to do the investigation and collect data. But this is a different factor and I am focusing on speed not mass.

The other variable you can change is the breaking distance by changing this you can change the surface, which the car can run on after it has come off the track. There are many materials such as sand paper, tarmac, wood and more. Sand paper would have no resistance, and tarmac would be unreliable as the car would have a bumpy breaking distance and would be different each time. I choose to use carpet as not many other materials would have such resistance, especially something like paper which would run on forever.

To make it a fair test I am going to use the same ramp and use the same carpet so the breaking distance isn’t too varied. I must use the same car as the mass of the car could vary to another, and the final speed could change affecting the breaking distance.

Hypothesis

I have come to a prediction from the preliminary experiment that the higher I release the car on the ramp the velocity will increase and so will the breaking distance. I predict that as the speed of the car increases the stopping distance will increase proportionally. Using this I predict that as the speed increases, the overall stopping distance will increase. Even though there is no thinking distance involved in the experiment that I am doing, there is still a braking distance force though.

This means that for the speed against distance graph I will hopefully get a perfectly straight line. For my graph though I do not get a perfectly straight line as there is the odd anomalous result. This result can be explained as maybe being the point on the ramp where the most acceleration and velocity is gained. When the car was going down a steeper ramp, its speed was affected more than down a gentle slope. To investigate whether all of the energy is transferred I can work out the gravitational potential energy (GPE) and also the kinetic energy (KE). If they are the same, this means all of the energy will have been transferred, if the KE is higher than the GPE then energy will have been lost and if the GPE is greater than the KE energy will have been gained. The energy lost will be turned into heat energy at points where there is a lot of friction and resistance and maybe into sound energy.

For my prediction I can use the expression for kinetic energy. KE = ½mv²

KE = ½ x 52.2g (weight of car) x 2.24² (quickest speed) = 130

We can also use Work done but for this I need to be investigating the affecting factor mass, - Wd = F x d.

Conclusion

My predictions were quite correct but I had some anomalous results which altered the appearance on the graph not making it a complete straight line, deviating off either decreasing or at one point increasing. I cannot make a firm conclusion with them. But generally the results all fitted to my predictions. Before the anomalous results, there is quite a straight line. There are things in the experiment I would have changed however.

Use a heavier car so the bumpy terrain would not be as noticeable
Or to this matter use a different ramp
Use a more streamlined car that loses lees friction
With a new ramp, use a smooth curve which would not lose speed and gradually change the direction of the car.
I would do each experiment many more times so when averaged it would get rid of the anomalous results.

Evaluation

My predictions were close but not close enough as there were around 6 anomalous results. I can’t make a complete conclusion, to do this I would have to redo the experiment making use of the alterations recommended in the conclusion. Also I would need a generally more controlled environment; I could use a real car and use a different material of a runway. I would also look at all the possible variables including the mass. This would be great as I could plot graphs against each other making a fair test having a lot more data.

In my preliminary experiment I have only taken ten results, because it is a plan and I have only looked at one affecting factor the speed. In the real investigation I will take a total of 32 results. I will obtain 2 results for each experiment and can then get an answer by averaging both results.

There were some results that were correct to my prediction. Most of them can be explained. In the graph of speed against distance, there is obviously good results at the beginning, but then as the bottom of the ramp gets steeper, it starts to affect the distance greatly.