Compression:
When it came to compressing the ball I had to devise a way to apply an even force on the ball in a linear way. This proved to be difficult at first; however I overcame this by devising a piece of apparatus that would do just this. On carrying out the test, I found it to give good results.
Variables:
There is only one variable in my experiment, which is temperature. I will be changing the temperature from 0-100°c in 10°c intervals, using a water bath. I will begin by preparing the apparatus, and then cooling or heating the water to the required temperature and then submerging the squash ball into the water for 2 minuets. I have chosen two minuets because I feel that this is long enough to heat or cool the squash ball to the desired temperature. I will then remove the squash ball and carry out the necessary test. When testing, I will ensure that the test takes as shorter amount of time as possible, due to the effect of cooling or heating created by the air. Once the experiment has been conducted, I will record the results and move onto the next temperature or test. By altering the temperature of the squash a number of factors are changed. Macroscopically, the stiffness of the rubber is changed, when cooled the stiffness of the rubber increases as the ball becomes less malleable. However when the temperature of the ball is increased, the stiffness decreases and the rubber becomes more elastic. This leads onto what is happening inside the ball, microscopically the pressure inside the ball is increasing. When the ball is heated, the air inside the ball expands at a greater rate than the ball itself, therefore increasing the pressure.
Safety:
In my experiment I will be using hot and boiling water which proves a potential hazard. I will ensure that due care is taken when handling the water not to spill it. I will not be using any large weights (4kg) and no electricity is involved.
Experiments:
Throughout the 4 tests, I paid due attention to accuracy of results and carrying out fair tests. I made sure that every experiment and test that was conducted was done exactly the same as the rest. I also ensured that the constants in the experiments, the weights, ruler, apparatus, thermometer and of course squash ball were all kept constant. By sticking to this I guaranteed that I would gain reliable results and conduct a fair test.
Height of bounce:
From my preliminary testing, I predicted that the height of the bounce would increase proportionally as the temperature increased. From the graph below and the table of results, we can see that my hypothesis was correct.
Procedure:
I began by setting up the apparatus shown in the photo below, which consists of a retort stand, boss, clamp, 1 meter ruler and a beaker with thermometer. Once all was set up, I brought the water in the beaker to the required temperature and then placed the squash ball inside the beaker for 2 minuets. Once the ball had been cooled/heated, I held it 500mm from the surface of the table (measured to the bottom of the ball) and then dropped it, measuring the height o the first bounce to the top of the ball. I then heated to the water by 10ºc and repeated the procedure in the same way until all the temperature intervals had been completed
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Results:
From the graph we can see that the results, when plotted form a straight line. This means that as the temperature is increasing, the height of each bounce is increasing with it as a constant and proportional rate.
Observations:
When carrying out the procedure at 80ºc I pulled the ball from the water and placed it on a towel. I then dropped the ball from 500mm but didn’t get a very precise reading, and therefore repeated it quickly. When I repeated the drop, I expected the initial measurement for the height reading to be marginally lower than that of my first due the temperature of the ball dropping, however, this was not the case. I noticed that the bounce was actually higher, which baffled me. I proceeded to test the ball again at 80ºc when it was both wet and dry and again, the dry ball bounced higher. This made me think. I came up with the idea that what may have happened is that when the ball is wet, i.e.: has water on the surface of the ball, a membrane of water collects at the bottom of the ball. This membrane cushions the impact of the ball and absorbs some of its kinetic energy. Thus, on the return journey (back up) the ball leaves the surface of the table at a lower velocity (compared to a dry ball) and consequently reaches a lower height. The diagram over page explains;
To replicate the effects the drop would have on the squash ball under standard conditions, I re-tested all the temperature intervals with the ball dry.
Number of Bounces:
Procedure:
Testing the number of bounces at each temperature interval was conducted at the same time as the height of the bounce. Once I had carried out the height of first bounce test, I placed the squash ball into the water again for a further 2 minuets to allow the ball to reheat to the correct temperature and then dropped the ball from 500mm and counted the number of bounces. Below are the results for this test and the graph showing the results.
Results:
Again, from looking at the graph, we can see that the number of bounces against temperature graph is very to similar to that of the height of first bounce to temperature graph. The line is linear, and therefore the results correspond to each other. This also shows that the temperature is proportional to the number of bounces.
Diameter of ball:
Procedure:
In this test, I decided that due to size I was measuring (approximately 40mm) I would use a digital verner calliper, which measures to 100th of a millimetre, this way, I would be able to measure the change in diameter of the squash ball to a high degree of accuracy. I began by heating water to the desired temperature and then placing the squash ball in the water for 2 minuets. When the ball had been heated I measured it with the calliper and then recorded the reading. Each time I measured the ball, I measured it from the same point on the ball each time, in case there were any permanent irregularities in the ball. I measured from the yellow dot to through the centre to the other side of the ball each time. Below are the results I obtained and a graph showing these results.
Results:
From analysing the results and the graph, we can see that a much more complicated line is achieved. From 0ºc to 10ºc we can see a gradual increase in the line, although by 20ºc the line beings steeping and the diameter is increasing at a greater rate per temperature. At 50ºc the graph line flattens out again until at 80º the line increases considerably up to 100ºc. This sudden increase at 80º again made me think and I came up with the conclusion that it must be the elastic limit of the rubber. When the ball is heated at conserved temperature >70ºc the ball behaves normally, however when the ball is heated beyond this point, it begins to disobey hook’s law and begins elastic deformation. After I had completed this test, I carried out an extreme heat test by placing the ball into ethylphenylamine, a non harmful liquid used to determine the melting points of chemicals. I heated the squash ball in the liquid to 160ºc. When I removed the ball from the liquid, the diameter of the ball was 43.18mm. This was not surprising as I was expecting there to be a large difference between this result and that of the one at 100ºc. However, the main point of this extreme test was to see if the elastic limit had been reached, and to see if the ball had deformed. After I had measured the ball at 160ºc I allowed it to cool overnight and ‘adjust’ to room temperature. Before I began even preliminary testing, I measure the ball at room temperature. It measured 40.44mm. When I re-measured the ball at the end of the investigation it measured 40.61mm. This proved my point that the ball had in fact undergone elastic deformation and the rubber had passed the elastic limit. After looking on the internet, I found that squash ball rarely reach temperature greater than 45ºc during aggressive play, and this suggests that the balls are not designed to cope with temperature higher than say 60ºc. This information also supports my theory.
Compression:
Procedure:
When I decided that I was going to compress the squash ball at different temperature, I was immediately faced with a dilemma. I needed a way of compressing the ball in a linear way so that an equal force was applied directly to the ball. The diagram below shows more detail;
From the diagram, we can see that unless I manage to do the impossible, (occasionally I may, but not today), and balance the weights on the ball and measure the compression, then I will have to devise a way of compressing them with equal force, but means of apparatus. The photo below shows the apparatus I designed and built to compress the ball;
It consists of two circular discs of wood, conjoined by a piece of wood to form a piston. The piston is then connected to a plate on which the weights will sit. The squash ball is placed inside the tube and the piston is placed down the tube until it is resting on top. The ruler is then moved up beside the plate and the starting measurement is recorded (height from surface to bottom of plate). The 40N is then loaded on top of the plate and the final height is recorded. The difference between the two is the compression in millimetres.
The apparatus worked very well and the results I gained agreed somewhat with my hypothesis and preliminary testing. Below are the results I obtained and a graph showing the temperature against the compression;
Results:
From examining the graph, we can see similarities between it and the graph showing temperature against diameter. Notice the way the graph gets steeper and then flattens and towards the higher temperatures becomes more exaggerated. This shows a connection between this graph and that of the diameter change graph.
Conclusion:
From conducting this investigation I have learnt a number of things (mainly about squash balls!!) Throughout I have been cooling and heating the squash ball to temperature beyond what it was ever really designed to cope with, which undoubtedly will put unwanted stress and cause deformation of the bal over time, and this factor had been taken into account, I have heated and cooled the ball many times and toward the end of the investigation I did notice some slight cracking of the ball and loss of colour. I have found that at higher temperatures;
- The ball has a higher internal pressure
- Increased diameter.
- Has greater kinetic energy and therefore bounces higher.
- Passes its elastic limit at around 60ºc.
In reality, a squash ball would not come under such extremes, however, the purpose of my investigation was to discover factors concerning the elasticity of a squash ball and I feel that I have exhausted all areas of this and have conducted fair and reliable investigation.