Therefore I think that the hotter the ball is, the higher its bounce height will be. I think this because I know from my background scientific knowledge that when the gas inside the ball heats up, the volume of the gas expands and the molecules will move faster which will cause them to hit the sides more often and harder. This makes the rubber expand and store more elastic energy. This would mean that the bounce height would be bigger because the more stretched the rubber is, the better it converts elastic potential energy into kinetic energy when the ball hits the floor and causes the ball to bounce higher. Also, the hotter the ball is, the firmer it is and the quicker it gets its shape back, therefore it loses less energy and then has more energy to use to bounce higher. Therefore I think that the lower the temperature of the ball, the lower the bounce height because I know from my background scientific knowledge that the molecules are moving slower and therefore won’t hit the rubber as often or as hard as at hotter temperatures. This would mean that the rubber wouldn’t be as good at storing elastic potential energy and converting it into kinetic energy when the ball hits the surface. The bounce height for all the temperatures will be much less than the original dropping height because energy is lost converting elastic potential energy into kinetic energy.
Risk assessment
To ensure a safe investigation I will make sure that nobody is around our working area so nobody could possibly get hit by the ball. I will also make sure that if the ball falls on the floor at any point I will pick it up straight away so that nobody can fall over it. I will also make sure that if the beaker of water, especially when it is hot water, will be in the middle of the table so that it can’t easily be knocked off spilling the water and creating a safety hazard of a slippery floor and broken glass. I will also make sure that if there are any spillages, I will clear them up straight away to prevent anyone slipping.
Preliminary work
I did some preliminary work to see what the best height to drop the ball from is and how long I need the ball to heat up in the water bath for it to reach thermal equilibrium. To investigate the length of time the squash ball needs to be kept in the water bath to reach thermal equilibrium I put the ball in the water bath at 30°C. I left the ball in the water for 1, 2, 3, 4 and 5 minutes. After each length of time I dropped the ball from a metre height and recorded the bounce height. When the bounce height no longer changed, the first length of time that gave this height is the length of time the ball takes to reach thermal equilibrium. I repeated each length of time three times to make sure I got accurate results and was able to get an average which I could look at to see at which point thermal equilibrium was reached. My results are shown below:
From this I can see that thermal equilibrium was reached at 3 minutes because this was the point that 28cm at a bounce height was reached and because the height didn’t increase more than 28cm it means that thermal equilibrium was reached. This is why I am going to leave the ball in the water bath for 3 minutes for it to reach thermal equilibrium.
To investigate a suitable height to drop the squash ball from, I dropped the squash ball at 20°C, 40°C and 70°C from various heights to find a height that worked well for all the temperatures. The heights I dropped the ball from were: 0.50m, 0.75m, 1.00m, 1.25m and 1.50m. To make sure the temperatures of the ball were accurate I left the ball in the water bath for 3 minutes as I knew from my previous preliminary results that 3 minutes is how long it takes the ball to reach thermal equilibrium. My results are shown in the table below:
From this I can see that 1 metre is a suitable height that I can easily record all the heights down to the lowest temperature (0°C) and gives a good bounce height for 70°C so it satisfies both ends of the range of temperatures. This height gives a good range of results so they can be shown easily in a graph and compared. I decided not to use the higher heights because even though they would also give a good range of results and I would easily be able to see the height of the ball at a 0°C temperature, it was unsuitable for my experiment because it meant that I would have to keep getting up onto the table to be able to reach the heights. This would cause more of a safety hazard and wouldn’t be appropriate for the experiment when a metre will give just as good results and result range. Therefore from my preliminary work I am going to use a drop height of 1 metre and leave the squash ball in the water bath for 3 minutes for it to reach thermal equilibrium.
Test Results
From these results I have been able to use the averages to plot points on a graph with a line of best fit so the information is clearly displayed and I can analyse the shape of the graph to see what it shows me. (Next page).
From these results and the graph I can see that the 10°C average result was an anomaly so we decided to do it again to check the results. The second time these are the results I got:
These results were much better and fitted in better with the line of best fit. Therefore I have decided to use my new results for 10°C and discount my old results as they are inaccurate and wouldn’t be of any use to the rest of the investigation.
Analysis of the results and what the evidence shows
The results/evidence shows that my prediction was right as they show that as the temperature increases so does the bounce height. I think this is because as I know from my background scientific knowledge that when the gas inside the ball heats up, the volume of the gas expands and the molecules move faster which will causes them to hit the sides more often and harder. This makes the rubber expand and store more elastic energy. This means that the bounce height is bigger because the more stretched the rubber is, the better it converts elastic potential energy into kinetic energy when the ball hits the floor and causes the ball to bounce higher. Also, the hotter the ball is, the firmer it is and the quicker it gets its shape back, therefore it loses less energy and then has more energy to use to bounce higher. The relationship of the points to the line of best fit shows strong positive correlation. As you can see from the graph the line of best fit is a straight line which shows that there is a strong relationship between the bounce height and the temperature of the ball.
This proves my scientific knowledge right because before the ball is dropped, energy is stored as GPE (gravitational potential energy). As the ball falls its speed increases and the GPE is converted to KE (kinetic energy), so half way through the fall half of the ball’s energy id GPE and half is KE. Just before the ball hits the floor all its energy is KE and none of it is GPE. Once the ball hits the floor, all the KE is converted to EPE (elastic potential energy) and some is lost as heat and sound energy which makes its energy less than its initial GPE. When the ball bounces back off the floor the EPE is converted back to KE, heat and sound. The ball will start to slow down as it rises and its KE is converted back to GPE but because some of its initial energy has been converted to heat and sound it will finish with less GPE than it started with. This is why the bounce height for all the temperatures is much less than the original height of 1 metre.
Trends and Patterns
As I have already said the shape of the graph is a straight line with all the points steadily increasing. All the points on the graph are close to or on the line of best fit this shows that my results were very accurate. This suggests there is a relationship between the bounce height and temperature which then suggests that there would be about the same difference between the height’s bounce heights.
The biggest difference between the temperature’s bounce heights is between 0°C and 10°C. 10°C is likely to be when the molecules of the gas inside the squash ball speed up and become much quicker than they were at 0°C and hit the rubber more often and harder. The rest of the bounce height differences are around about the same area except the 9.2cm difference which is also quite high. This may again be due to the molecules in the squash ball again really starting to speed up as the temperature goes from a warm state to a hot state. This shows overall that there is a definite link between the bounce height and the temperature of the ball and therefore showing that the higher the temperature of the ball, the higher the bounce height and the lower the temperature of the ball, the lower the bounce height.
Conclusion
The evidence shows that my prediction was correct as the higher the temperature of the squash ball, the higher its bounce height. As you can see from the graph the lowest temperature of 0°C gave an average bounce height of only 5cm which would be 5% of its original height. Whereas the highest temperature of 70°C gave an average bounce height of 58.4cm which is 58.4% of its original height. This proves my prediction right as not only can you see from the results that the bounce height increases as the temperature increases, you can then see from these results that it must be due to the gas inside the ball heating up, causing the volume of the gas to expand and the molecules to move faster which will caused them to hit the sides more often and harder. This made the rubber expand and store more elastic energy. This meant that the bounce height was bigger because the more stretched the rubber became, the better it converted elastic potential energy into kinetic energy when the ball hit the floor and therefore caused the ball to bounce higher.
Evaluation
I think that my results were as accurate as I could have made them with relevant safety points carried out and I got good, reliable, accurate results. The only anomaly I got was at 10°C because the temperature kept dropping which made the average too low. I decided to do the test for 10°C again and my results were much better. The average result for 70°C was lower than the line of best fit because I think that once the ball starts to reach the higher temperatures the ball can’t keep on stretching and eventually it will reach its maximum stretch and therefore it won’t bounce any higher, it will level out. The 70°C point looks like it would be the start of a curve to the levelling out of the bounce height. Other than that my results are very accurate as they are all very close to my line of best fit suggesting that there aren’t any anomalies although some points are further away from my line of best fit than others. These aren’t anomalies though because not every point will be exactly on the line of best fit because it would have to be extremely well controlled and that isn’t possible in classrooms and unlikely to be possible in the most controlled laboratories. There will always be differences in the results no matter what so therefore I believe that my results were as accurate as possible.
My investigation could have been improved by:
- Not doing the test over two lessons so all of the equipment would be the same.
- Making sure that all the preliminary work was done before I did the actual experiment.
- Making sure the temperature was kept exactly the same and not letting it drop or increase by even 1°C.
- Doing more tests to make sure I get a very accurate average.
- Being quicker between taking the ball out of the water bath and dropping
- Not allowing the squash ball to some to the surface of the water bath at some points, keep it below the surface to make sure it definitely reaches thermal equilibrium.
I think my results were very reliable even though it was done over two lessons so some of the equipment wasn’t the same but it wouldn’t have made much difference as all the equipment was mostly the same and were all accurate. At the lower temperatures such as 0°C and 10°C it was hard to keep the temperatures down in a warm room and had increased by a degree or two which could have made a difference to the bounce height. This would explain why the 10°C point was higher than the line of best fit. Other than that we were very accurate with keeping the water bath at the right temperature and this was shown by the closeness of the points to the line of best fit.
To provide additional relevant evidence I could:
- Use temperatures that go up in 5°C instead of 10°C so I would have more information to show the relationship between the temperature of a squash ball and its bounce height.
- I could have a better way of seeing the bounce height by having a video camera set up about a metre away from the experiment to see where about the ball bounced and then have another camera close up to see a closer reading of the bounce height. When I play back the video, I would put it on slow motion and show it frame by frame recording the heights until the bounce heights start to fall. Then I would take the maximum recording I had for that temperature and that would be the bounce height. This would be very accurate because I would see a very close up measurement and because it would be in slow motion and frame by frame it clearly showed the bounce height and could clearly be read from the bottom of the ball. This is more accurate than using your eyes because the ball would bounce very quickly and you only have a split second to read the height and is very difficult.