“The faster the car goes the longer it will take to stop.”
Prediction
I think that if the speed is greater the braking distance will be greater and vice versa. The car needs to get rid of its kinetic energy and the formula for kinetic energy is (½ X Mass X Speed ) so it will take more time to get rid of more kinetic energy caused by more speed. If two cars of the same weight of 800KG are travelling at 30mph and 60mph respectively it will take the car travelling 60mph 4 times longer to stop down than the car travelling 30mph. The reason for this is that (½ X 800 X 30) = 360KJ but when we work out the amount of kinetic energy transferred when the car travelling 60 mph (½ X 800 X 60) = 1440KJ. This shows us that it will take the car travelling 60mph 4 times longer to stop as apposed to the one travelling 30mph providing speed is the only variable. Also a car that travels faster has more inertial (mV) and so if it has more velocity it will take longer to stop.
Method
I think that taking results every 5cm will offer a good range of results which can be plotted on a graph easily and show a correlation. The way the speed will be altered is that the toy car we are using will be attached to a length of tape that will be made longer or shorter depending on what speed is wanted. The reason that the speed will alter is because the car is going down a slope, objects travelling down a slope will accelerate at a steady rate and keep on getting faster and faster rate until the slope stops or another variable alters acceleration. The way that I will make the car brake is by taking the slack and putting a weight at the end of it so when the slack runs out the car will brake and stop, the amount of more tape the car pulls through is its braking distance. The ticker tape will be held on to the car with blue tack. During each test none of these should be changed because if they are it will become an unfair test and the results will be meaningless. I think that the equipment that I am using will not give me continually similar results because it’s not a very good way of doing this investigation using a wooden block as a brake. So some results will not fit with the general set of results but that’s because of the equipment, however I do think that a trend will be found.
Results
This graph shows that the faster the car goes the longer it will take to stop. The line of best fit shows a strong positive correlation between speed and braking distance. I think that the car has accelerated at a constant rate and got faster and faster, so therefore taken longer to stop because more kinetic energy has to be transferred. The equation for kinetic energy is ½(MV ) so as the car accelerates more it will have more kinetic energy and will take longer to transfer it.
Here is a table showing the average braking distance for each speed that I measured. So these results definitely do show a strong positive correlation between speed and braking distance.
Another piece of scientific evidence that I can use as evidence to explain why the braking distance gets longer with a bigger range in-between each amount of slack is the formula F= ma; if the mass is a constant and the acceleration was more in one case then it would have more force and as a result take longer to transfer that force (in the form of heat).
I think that the results I have got prove my simple prediction of
“The faster the car goes the longer it will take to stop.” With the graph the line of best fit obviously shows a very strong positive correlation between speed and braking distance, even when just looking at the results table it’s plain to see. I can even prove this using the two formulas I have already talked about: If I take the car had 5cm of slack and work out the formula for it, then compare it with the results from the same formula for the car which had 30 cm of slack I am sure I will prove my prediction,
(½ X 0.0444KG X 0.05m ) = 5.55 X 10 J
(½ X 0.0444KG X 0.10m ) = 2.22 X 10 J
This shows that the car which had 10 cm of slack (travelling faster) had more kinetic energy and will take longer to transfer it. Also I think that the car travelling with slack of 10cm had twice as much speed than when it was at 5cm and subsequently would have four times as much kinetic energy. The reason for this is that is that the force of gravity is acting upon it and this is controlled acceleration; gravity’s force is 9.81mps . Some of the results did seem a little random and didn’t quite fit but that was because of the brake, if we were using much better equipment then I think that the results would follow a pattern nearly 100%.
Evaluation
The evidence that we got varied quite a lot, there was quite a lot of difference in the range of results, this table shows the range between the highest and lowest braking distance on each distance that I measured
So you see by this table that there was a big range between the stopping distances. There is a number of different reasons for this big range: Firstly what I thought was the biggest problem in the experiment was the brake, it was very unreliable and it took me several attempts to actually get a result for 30cm of slack because the brake couldn’t cope and just let all the slack through because the car had too much velocity; however this was because the ramp was on too high a gradient. Depending on where the slack was on the brake could mean that the car kept on going or stopped dead and this made some of the results unfair. Really I think that a good brake would have been something that caused a lot more friction and had the same amount of friction on each part of it. I think that for something like that a really coarse piece of wood would be good or maybe even some sand paper on the bottom but that might tear off the ticker tape. Possibly if the gradient of the ramp had been reduced then the results could have been a little more accurate because there wouldn’t have been as much force pulling the tape through and so it wouldn’t get pulled all the way through by the car’s force. I think that they were the only variables that I could have changed in this experiment.
Another way that we could have done it is by using a bike because it’s easy to get one because I have one at home and the results would have been a lot fairer and accurate because the brakes are of much better quality. Also other variables could have tested, such as thinking distance and gradient. However stopping suddenly on a bike is not such a good idea because it can lead to injury and it wouldn’t be very fair to try and use the brake only on half power for example.
I could use a real car but that would be very expensive and it would take a long time to get a lot of results, also we’d have to weigh it and I’d have to get some-one to drive it.
If we did any of these proposals I’m sure we would get a fairer test with more accurate results also it would make it a more realistic situation. Still I do think that the results that I got prove my simple prediction of
“The faster the car goes the longer it will take to stop” because the graph still shows a strong positive correlation. I have proved the formula of kinetic energy (½ MV ) so I think that this experiment has done what it was intended to do it’s just that it could have been done better and made into a more realistic situation.