For my fourth and final test I am going to try placing the balls in different temperatures of water. Making the balls hotter will only affect the balls that are hollow, but I will also test the hockey ball, which is solid to make sure of this. This is because the balls that are hollow are filled with gas. By making the balls hotter the particles inside the ball will gain more kinetic energy, so the pressure inside the balls will increase. This will make the balls harder and so they will get harder and so bounce higher (see prediction above).
To test this prediction I will heat beakers of water to various temperatures (0, 20, 40, 60, 80, 100°C) and leave the balls in these beakers for 1 minute. This should be enough time to allow the gas inside the balls to warm up. When we have fished the balls out of the water we will drop the balls from various heights (20cm, 40cm, 60cm, 80cm, and 100cm). We will drop each ball twice and then take an average. We will measure the height of the bounce in the same way that we did in the other tests. We will not perform this test on the tennis ball, even though it is hollow, because immersing it in water will give misleading results. This is because the water will make it soggy (because the cloth will absorb the water) and it will not bounce as high.
Obtaining Evidence
I have outlined the method for each of the tests that I am going to do above. The results obtained from each test are shown in the tables below. I have also included the weight of each ball and shown whether it is hollow or not.
Ball Weights:
Test 1: Do Hollow Balls Bounce Higher Than Non-Hollow Ones?
Test 2: Does The Height From Which The Ball Is Dropped Affect The Height Of The Bounce?
Hockey
Squash
Tennis
Golf
Table Tennis
Test 3, Do Bouncier Balls Take Longer To Stop Bouncing?
Test 4, How Does the Temperature of the Ball Affect the Bounce of the Ball?
Hockey 0 Degrees Centigrade
20 Degrees Centigrade
40 Degrees Centigrade
60 Degrees Centigrade
80 Degrees Centigrade
100 Degrees Centigrade
Squash, 0 Degrees Centigrade
20 Degrees Centigrade
40 Degrees Centigrade
60 Degrees Centigrade
80 Degrees Centigrade
100 Degrees Centigrade
Analysing Evidence and Drawing Conclusions
Test 1: My results for this test were interesting. I said that the hollow balls would bounce higher than the non-hollow balls, and in some cases I was right. The exception was that the golf ball, which is non-hollow, bounced the highest out of all the balls. This could be because it is made mainly of cork, which is quite a bouncy substance, or it could be because our measurements are inaccurate. I suspect that it is because it is made of cork because it is a lot higher than the result for a tennis ball.
Another exception is the result for a squash ball, which is hollow. It was the lowest result that I obtained, even though it is hollow. I think that this is because it is so soft. The design of it allows much the impact energy to be absorbed by the sides of the ball when they squash in, and so meaning that less energy is transformed into kinetic energy, so the ball has a lower bounce.
The other unusual result is the result for the tennis ball. Despite a tennis ball being heavier than a table tennis ball, the table tennis ball bounced higher. The only reason that I can think could have caused this result was that a slightly dud tennis ball was used and that this effected the result, or that my prediction was incorrect.
Apart from these abnormal results the rest of my results for this test were quite good. The non-hollow hockey ball that I expected to be low bouncing was, and the hollow tennis and table tennis balls that I expected to be high bouncing were.
These results do not really support my predictions for this test. I said that the hollow balls would always bounce higher than the non-hollow balls, and I was wrong. I do not think that my results were inaccurate because I got the same shape graph for both this test and the next test (see below). Neither was I correct in saying that the heavier hollow balls would always bounce higher than the lighter hollow balls. The table tennis ball, which was the lightest ball on test, bounced the highest out of all the hollow balls. This was also true of the non-hollow balls. The hockey ball, which was the heaviest, bounced a lot lowers than the golf ball, which was very light in comparison.
Test 2: As you can see from the best fit lines that I have drawn on my graph, my results for this test were very accurate. I had only one result that was wildly inaccurate (golf ball dropped from 0.75m). All the other results were very close to my best fit lines.
These results also support my predictions very well. Only one result was inaccurate (the one that I mentioned above) and did not support my predictions. I said that the higher a ball is dropped from the higher it will bounce back up. This was true in all but one case, and I suspect that was caused by some inaccurate measuring. The results from this test also support my results from test one, as the golf ball bounced the highest, the table tennis ball bounced the second highest etc.
Test 3: My results for this test were generally fairly good. In all but one of my tests the ball that bounced the highest in the first test took the longest to stop bouncing in this test. The one exception was the table tennis ball, which bounced the second highest but took the longest time to stop bouncing. I think that this was because the table tennis ball is better than the golf ball at conserving energy, so less energy is lost on each bounce and the ball takes longer to stop bouncing. I think that the table tennis ball did not bounce the highest because it has less energy because it was so much lighter than the other balls. This would explain why the golf ball took the longest to stop bouncing even though it was not the heaviest ball. The golf ball that bounced the highest took the second longest to stop bouncing in this test. All the other balls were in the same `positions` in both tests. If you look at the graphs for this test and the first one you will see that they are a very similar shape, which would suggest that my results were quite accurate.
These results supported my predictions quite well. I said that the bouncier a ball is the longer it will take to stop bouncing. This prediction was correct in all but one case (see above), and so I think I can say that my prediction for this test was correct.
Test 4: The results for this test were very good and seemed to prove my predictions. If I firstly look at the results for the squash ball they would seem to be quite accurate and they would seem to support my prediction. In every case the hotter the ball is the higher it has bounced. Apart from the results for 0 degrees centigrade, the extra amount of bounced as increased at a fairly steady rate, which would again suggest that these results were accurate?
As I have already said, I think that this happened because the heat gave the particles of gas inside the ball more kinetic energy and so increased the pressure. The increase in pressure made the ball get harder and so bounce higher (see prediction 1). I think that the ball bounced lower than normal when cooled to 0 degrees centigrade because the pressure inside the ball decreased in so made the ball softer than normal and so made it bounce lower than normal.
The results for the hockey ball are also quite good. At first glance they may appear to be very inaccurate and jumbled up, but if you study them more closely you will see that they are quite good. In my prediction I said that changing the temperature of the ball would not affect a non-hollow ball, and I was right. All the results for the hockey ball are close together, suggesting that any differences may be because of inaccuracies in the measuring or because the ball bounced inconsistently. The differences in the height the ball bounced become more obvious the higher the ball is dropped from. These results also suggest that my predictions for test two were correct.
Overall I was pleased with the results that I obtained from these tests because they supported by predictions for this test and some of the other tests very well. The reason that I did not test the hollow table tennis ball was because I did not have time to, but I suspect that had I done so the results I would have obtained would also have supported my predictions.
Evaluating Evidence
Test 1: I thought that I worked well during this experiment. I think that I obtained accurate results from this test, although my results did not support my prediction. If I had more time to conduct this experiment I might have tried the experiment with more types of ball. I could also have taken three or four readings for each experiment and then taken an average. This would have probably produced a more accurate result, unless all the readings were inaccurate.
I cannot be 100% sure that these results are 100% accurate because there is a chance that the measurements could have been measured inaccurately. When measuring something with only the human eye there is always a chance that the measurements could be inaccurate because the human eye is not the most accurate measuring implement that there is. If I wanted to be completely accurate I could try the experiment again, but using light gates to measure the height of the bounce. However it was not really that practical to use light gates for our experiment because we did not have time to keep setting the gates up.
Test 2: As I have already said in my conclusions for this test, I think that my results for this test were accurate. I think this because all bar one of my results were very close to my best fit lines. I think that what I said in the conclusion for the previous test is true here; the results seem to be accurate, but I cannot be 100% sure that they are 100% accurate because there is always a chance that human error could creep in.
If I had more time to conduct this experiment I think that I would try to use light gates, as this would probably make my results more accurate by eliminating the `human factor`.
I think that these results are accurate enough to support my predictions, as they are all very close to the best fit lines on my graph. There are not many ways in which I could improve my results for this test, except by taking more readings before calculating the average result.
Test 3: I think that my results for this test were generally fairly accurate. However I was a little surprised that the golf ball, which bounced the highest, did not take the longest to stop bouncing. That honour went to the table tennis ball. However I think that result can be explained (see conclusion for test 3) quite well.
Again I cannot be total sure that the results are 100% accurate because there is always a chance that human error can creep in. Another thing that could affect the results is that it is very hard to start the stopwatch at exactly the same time as the ball is dropped. There are only two ways that these results could be made more accurate. One way would be to get some sort of automatic set-up that would drop the ball and start the stop watch at exactly the same time. Another way would be to have the same person dropping the ball and starting the stopwatch. This would be easier to do, although perhaps not as accurate.
Overall, I think that my results were accurate enough to support my predictions, and I think that they do.
Test 4: I was very pleased with my results for this test. Although it looks as if the results for the hockey ball are inaccurate they are really what I expected. As I have already said, the hockey ball is non-hollow, and so changing the temperature of it should not effect the results, and it did not.
I think that although the results for this test were accurate, they were not as accurate as some of the other results that I obtained. The results for the squash ball when it was at low temperature were a bit out when compared to the other results. The other results all increased at a steady rate (1 metre at 20, 60, 80 and 100 degrees centigrade are all separated by roughly the same vertical alignment), but the result for 0 degrees centigrade was much lower than the other results. I think that this could have been because it was so hard to measure a ball that is only bouncing a few centimetres above the ground. When you are trying to measure distances this small with your eyes, errors are bound to creep in.
Overall I think that the results that I obtained for this test were accurate enough to support my predictions. The reason that I did not test the hollow tennis was because the cloth on the tennis ball would have absorbed the water and given misleading results. If I had wanted to test a tennis ball I would have had to find some other way of heating the ball, perhaps by putting it in an oven. The reason that I did not test the hollow table tennis ball was simply because I did not have enough time to.
If I had more time to repeat this experiment the first thing that I would do would be to test the table tennis ball. Although this ball was not tested, I still think that my results were accurate enough to support my predictions.
Overall Conclusions: I was pleased with the way that I worked in this investigation, and I think that I obtained some accurate results. Some of my predictions were more accurate than others. I hope that this investigation will earn me a good mark, as I have put a lot of effort into it. I enjoyed doing this investigation and I am looking forward to my next one.
