I will vary the height of the ramp using the blocks, which in turn will vary the speed of the car. I will measure d that will be equal and kept constant at 100mm.
Therefore to find the speed of the car I will use the formula:
Speed = Distance (d) of card / time on light gate
Then I will measure the stopping distance from the base of the ramp.
I will repeat the readings 3 times and find the average stopping distance over 8 different speeds. A preliminary test showed that the maximum height or blocks is 8 because after that the front of the car hits the table to hard and it doesn´t result in an accurate increase from the height or speed before.
Qualitative Prediction
I predict using simple common sense and logic that the cars stopping distance will increase as the speed of the car or height of the ramp are increased. I think this will happen because by increasing the ramp size and therefore increasing the speed of the car you are increasing the amount of K.E., Kinetic Energy that the car has. Therefore having more energy to overcome frictional forces acting on the car will result in a larger distance cover, or larger stopping distance.
Also the law of conservation of energy says that:
Loss in KE of car = Work done by frictional forces
Or ½ MV2 = F x D
Therefore if F (frictional forces) is assumed as constant then
D = (½ M/F) V2
But I think that F will change through out the experiment because of heating effects on the axles of the car and wheels. Because as the car increases in speed it will therefore turn the axles faster and this means that the axles will come in contact with the chassis more often therefore generating more friction between the axles and the car, I think that F will change.
So D ? V2
I.e. stopping distance is proportional to (speed) 2
So if speed is doubled i.e. v = 2v; stopping distance will quadruple
Because
D ? V2
D ? (2V) 2
D ? (4V)2
Obtaining Evidence
Result Table of Experiment
This is an anonymous result because all the others are above 530 but this result is below 500. This is an error. To ensure accuracy through out the experiment I repeated any results when the car hit the ruler or the light gate. When we increased the speed to a certain amount the car gradually curved towards the ruler, which it eventually hit. Due to this fact I had to ensure the car was let go of straight down the ramp and not at any slight angle. This was very hard to keep constant because the angle of the car looked straight enough to the eye but was probably out.
Also to ensure accuracy we had to make sure we looked down as close to a 90-degree angle as possible when measuring stopping distances off the ruler, this might of caused error in the results. We also used a separate ruler to measure across from the front of the car to the meter ruler, this was also hard to keep at a right angle to the car because the bonnet of the car was curved. Sometimes I accidentally pushed the car when carrying out this operation and therefore repeated that measurement. Also we had to ensure that the light gate was positioned correctly. The car had to pass through on the flat table and not at an angle. If it did pass through at an angle, this would of created an error in the results, because the amount of card that passed through the light gate would be more than if it was at an angle rather than on a flat table. Therefore 'd´ or distance which was required to work out the speed would not been kept constant and therefore would of caused an error in the results.
Analysis
The information presented here in graphs shows clearly that as you increase velocity the stopping distance of the car increases.
Conclusion:
I conclude that with reference to the graphs that frictional force increases as you increase the velocity. This is shown in graph 2 where velocity increases in a curve not a straight line, therefore there is another variable involved, e.g. friction.
Evaluation
The method could be improved considerably because there is too much room for error when conducting the experiment. Although the results were fairly reliable and gave reasonable graphs there could be areas that could be improved within the method. There was one identifiable anomaly, which has been high highlighted in the obtaining section. This anomaly could have been caused by an inaccuracy when doing the experiment, this could have been caused by accidentally pushing the toy car when letting it go down the ramp. Or also the car might of passed through the light gate at a slight angle and therefore increased the value for the distance, this would of caused an error.
The method used was fairly reliable as I used a light gate to measure the speed, which is much more accurate than other methods, which would involve manual timing.
But also there are a lot of things that could be improved for example-using blocks to support the ramp could have caused an error because they might not have been exactly 10mm thick, therefore causing an inaccurate increase in height. This would probably not of showed up in the results, also the positioning of the ramp was often moved this could of altered the angle o the ramp which could of caused error. One of the most obvious changes which could be improved is the release of the car down the ramp this was done by hand which would have caused inconsistencies in results. Another part of the method that needs to be improved is the act of measuring the stopped distance of the car. This also was done by hand which could cause significant error because of the inaccuracies involved with looking down at the ruler and reading off a value. To improve the point made about releasing the car I would set up some sort of clamp with a solenoid to release the car electronically therefore eliminating any human error. Also stopping distance could be measured electronically by using several hundred tiny lasers or light gates set up in millimeter intervals, just like a ruler along the area where the car would run. Or there could be tiny magnets set up along the ruler and a reed switch attached to the side of the car and as it passed along side the ruler depending on how many times the reed switch was broken it would calculate a distance. Then a measurement could be digitally read of a display, which would eliminate any human error in looking at a ruler. But these ideas are far too unpractical to do at school and would be very time consuming to set-up. Also to improve on the height adjustment of the ramp could be done using pneumatic pistons to lift the ramp up and down to the exact height wanted.
