What factors affect the bounce height of a squash ball
What factors affect the bounce height of a squash ball?
Sam Miranda S5A
My objective for this experiment is to see how height affected the bounce of an ordinary squash ball. The heights which I intend to drop my single squash ball from will be my only variables. I was considering selecting temperature of squash ball as the variable, but thought this would be particularly difficult to maintain a fair test due to the excess apparatus.
A squash ball is made up of two rubber halves. It contains a certain amount of compressed air- certain squash balls due to playing conditions have less compressed air than others. Some of this compressed air is lost when the ball comes in to contact with another object. On impact, the ball also heats up slightly, and therefore the more the ball comes in contact with something with considerable force, the hotter it gets. This is why quite a few balls have to be used in a squash game. When the temperature of a squash ball rises, the pressure of the air inside the ball increases.More pressure inside a ball, means that it will bounce back higher when it comes in contact with something, therefore the hotter it gets the higher it will bounce back.The higher a squash ball is dropped from, the higher it will bounce back up. This is because when they are dropped from a higher position, they have more gravitational potential energy (GPE). When the ball comes in contact with an object, all this GPE is converted into kinetic energy, and therefore the higher you drop a squash ball from, the higher it will bounce back up.
In order to inform my plan and method, I had to perform a preliminary experiment. This would give me a signifcant idea on the outcome of the main experiment, and give me hints on how to improve it.
I took a "medium pace" black squash ball and set up a vertical metre stick attached to a bosshead and clamp. At 20cm height intervals up to 2 metres, I dropped the black squash ball and recorded the height bounced in centimetres with the naked eye. In order to be precise, I measured from the bottom of the squash ball at all times. To make sure the ball was dropped exactly from the heights, I used a set square as a temporary balance, before releasing it.
I predicted that the higher the ball is dropper from, the higher it will bounce. This is because when a ball is dropped from a higher height, it has much more GPE than if it is dropped from a lower one. Therefore all this GPE can be converted into kinetic energy, allowing it to bounce higher. As well as this, when a ball is dropped from a higher height, the ball is compressed more when it comes in contact with the ground, and therefore the compressed air can again make it bounce back higher.
Here are my preliminary results in a table.
Height from which squash ball was dropped / cm
Height that squash ball bounced from desk surface / cm
20
5
40
8
60
1
80
4
00
8
20
20
40
22
60
25
80
29
200
30
These results seem to fit my prediction well, although I feel for my main experiment I could conduct it with a greater degree of accuracy. I will ...
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Here are my preliminary results in a table.
Height from which squash ball was dropped / cm
Height that squash ball bounced from desk surface / cm
20
5
40
8
60
1
80
4
00
8
20
20
40
22
60
25
80
29
200
30
These results seem to fit my prediction well, although I feel for my main experiment I could conduct it with a greater degree of accuracy. I will record three bounce height measurements, in order to achieve an average. From this I can discount anomalies with ease. I will naturally be more cautious before each drop, making sure the set square is exactly in line with the specific drop height. I have decided not to drop from such low heights because the bounce was very low, and I couldn't read it very well. This made the results quite inaccurate as to get very precise results for such a low bounce height, I'd have to have measured it to about three decimal places.
Main Investigation
Consant Variables to make it a Fair Test
) Temperature is a big variable in affecting the bounce of a squash ball. Temperature affects the pressure within the squash ball, which affects how much it bounces; the kinetic theory is thus used. As temperature increases the gas molecules gain more energy due to the heat energy and it is converted to kinetic energy. The molecules, with more kinetic energy, have more frequent collisions with other molecules and the walls of the squash ball, thus pressure is increased. The increase in pressure means that the squash ball will bounce more. A change in temperature would change the outcome of the experiment dramatically, so I am conducting the experiment at room temperature.
2) The surface the ball is dropped onto is not a good variable to investigate. Basically different surfaces will affect the bounce, like a spongy surface will absorb the bounce of the ball and you won't be able to tell the difference with each of the different balls. A hard surface will have a different affect on how the ball bounces, it will bounce more so this is a good surface. I intend to bounce the ball from a wooden desk surface all the time.
3) Say that the two circles were eyes, and they were both reading the bounce of that particular ball,then they'd both have read it from different angles and therefore had gotten different results. For that reason, the eye level has to be consistent.
My changing factor
The height the squash ball is dropped from is my changing factor. At increasing heights the bounce will be higher than at lower heights as the ball will have gained more velocity due to acceleration due to gravity.
Method
* Take a metre ruler and clamp it to a stand using a bosshead and clamp
* Take one black squash ball
* To experiment with your changing factor, adjust the bottom of the squash ball to different heights, using a set square or a ruler for precision
* Release the ball and record the height bounced with the naked eye
* Repeat three times in order to obtain an average
* Record the results and plot a graph in preparation for analysis
For my main experiment I recorded three results from each height station, as my preliminary informed me that this would be a sufficient degree of accuracy. There were few specific areas which reflected a great deal of change and interest, so I decided not to focus on any particular area, and opt for breadth rather than depth. We will communicate our results by using a table, and also displaying them on a graph. This will help us see any anomalies or faults within the experiment, and let us make changes or amendments where appropriate.
Analysis
My results show a distinct pattern- that as the height from which the squash ball increases, the average bounce height increases, for instance the average bounce height at 20cm is 4.3cm, and the average bounce height at 40cm is 7.3cm. The approximate difference from bounce heights as the drop height increases by 20cm is between 3-5cm. There are few anomolies, but between 100cm and 120cm drop height there is a change of just 2cm in average bounce height. This compensates for my vague 'S' shape curve on my graph's best fit line. I recorded three bounce heights at each drop height, in order to obtain an average. I have noticed that the third drop always seems to produce the higher bounce, and the first drop to produce the lowest bounce. For instance, at a drop height of 100cm, the first bounce height was 18cm, and the third 20cm. We know that proffesionals hit the ball hard against the wall at the start so it bounces more, and although on a relatively minute scale, we could be doing the same thing. As we bounce the ball on the wooden desk, the ball also heats up slightly, and therefore the more the ball comes in contact with something, the hotter it gets. When the temperature of a squash ball rises, the pressure of the air inside the ball increases. More pressure inside a ball, means that it will bounce back higher when it comes in contact with something- the desk in this case. This is a scientific theory that can offer a reason as to why the third drop produced a higher bounce height, but it is unlikely it was a significant contributor in a small scale lab experiment. What is more likely, is that as my eyes became more accustomed to reading each bounce height from a specific drop height, they became more effective at recording the exact bounce height. It is possible that the bounce height recorded in the first drop was in fact incorrect due to a reading error.
My best fit line on my graph shows that the average bounce height is directly proportional to the height dropped. At a height of 120cm, the slight anomalies in the results are show by a change in gradient, as the graph takes on a vague 'S' shape. From a height of 160cm the graph resumes a steeper gradient. My line of best fit is close to the majority of results, indicating its successful and reliable nature.
The results fit my prediction quite well. When dropped from an increasing height, the ball gains more gravitational potential energy which means that when it hits the floor it can turn into kinetic energy, allowing it to bounce back higher than when it is dropped from lower down. When the ball collides with the desk, the ball becomes deformed. The ball is elastic in nature, the ball will quickly return to its original form and spring up from the desk. The ball pushes on the desk and the desk pushes back on the ball, causing it to rebound. Neglecting friction for the ball, the potential energy before you drop the ball will be equal to the kinetic energy just before it hits the ground.
As well as this, when dropped from higher, the ball is compressed more then from if you'd drop it from lower down, allowing it to bounce back higher. Though this may happen, I believe there will be a point or a limit at where it would stop, as if this were the case then it could bounce x amount of metres, which it can't.
Evaluation
I found that my results were quite accurate, as they fitted in with the laws of physics that we explored, as well as generally being quite well done.
I believe that the way we conducted our experiment was sufficient for the amount of equipment that was available to us. As well as this, we were exploring a wide range of data, the results were consistent, and as we saw had a pattern showing that they were probably correct. They also matched the prediction that I put forward. The quality of the evidence was quite high, as you can see, and there are no signifacant anomalies to note down. The experiment was suitable to the question in hand, yet certain improvements could have been made. My line of best fit is close to nearly all the points, and we cannot call the recording made at a height of 180cm definitely anomolous. There is a clear patter, as when dropped from an increasing height, the squash ball bounces heigher. The ball gains more gravitational potential energy which means that when it hits the floor it can turn into kinetic energy, allowing it to bounce back higher than when it is dropped from lower down. My results and graph supports this statement, as at a height of 20 cm, the ball bounced an average 4.3cm, and at a height of 200cm, the ball bounced an average 36.7cm.
We could have perhaps had two people reading the measurements, so that we got a more accurate answer, not just the point of view from the one person. As well as having two people taking down readings, we could have one at a different angle, taking the average and then finding the height of the ball, nearly exactly. The accuracy of the human eye when recording the differenes between relatively small changes of height is questionable. To find the exact rebound height of the ball, I could have painted it in a specific colour, and then the wet paint make a mark on the metre stick, indicating its precise bounce height. An alternative method is to video record the experiment up close so it can be stopped when the ball is at its highest point and the correct measurement can be seen and will increase the reliability of the data obtained.
I was disappointed with my preliminary experiment in the sense it gave me little instructions on what to change. All I discovered was that to improve accuracy I needed to record three results at each heigh in order to obtain an average.
The first thing that I noticed was that by dropping it by hand it was very hard to get from the height that I was dropping it then get down to see how high the ball bounced. If I were to repeat the experiment at school lab level I would require a method where I could stay low down to see the bounce of the squash ball but release the squash ball when I wanted it to. Perhaps I could have used some tongs with a piece of string, the forceps to hold the ball then the string to release the tongs so the ball drops. By employing this method it would mean just the ball being dropped and no other forces other then gravity acting on it, as before I may have put some spin on the ball making it bounce in a direction which would affect results.
We could have used different balls, as well as changing the people doing it, gathering information from different points of views. We could have also repeated the experiment in a vacuum so that there would be no air resistance.
For further experiments, I believe it would be interesting to test how temperature effecs the bounce height of a squash ball. We could mirror a match situation, where professionals hit the ball very hard to heat the ball up. We could use difference surfaces and investigate as to whether the bounce height changes, or even wrap the squash ball up in different materials.
