Preliminary Work
I decided to do two experiments previously to see what height from which the ball is dropped and what type of surface would be suitable. I found out that the best height to drop the ping-pong ball would be 50 cm, because the potential energy at this point is quite high at 1200 J; therefore I should receive a good set of readings. I think that a set of eight readings would be suitable; therefore I will start at 50 cm and take a set of readings at 60 cm, 70 cm, 80 cm, 90 cm, 100 cm, 110 cm and 120 cm. I found out that the most suitable surface would be a wooden bench, because it is a hard surface and it absorbed less heat and sound energy on impact, therefore the ball bounced to a reasonable height.
Safety
Looking back at my equipment list and method I can see that there are not any obvious hazards; therefore the only precautions I can take are that I will wear goggles and I will not play around with the metre ruler or ping-pong ball while experimenting.
Fair Test
In order to conduct a reasonably fair test I will have to control certain points. These are,
- To make sure that the height is accurately read each time. I will use a ruler as a marker instead of relying completely on my naked eye in order to achieve a certain degree of accuracy.
- To make my results more precise I will repeat the experiment three times and take a set of five readings for each height every time.
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To ensure that the angle of the ruler is the same each time at 900, by using an angle measurer.
- To use the same equipment each time i.e. ping-pong ball, metre ruler, etc.
- To use the same wooden bench for every reading.
- To make certain that the mass of the ping-pong ball is kept constant at 2.4g.
- To keep the temperature of the ball reasonably constant each time. To do this I will restrict myself from holding the ball in between readings as the heat from my clasped hand may alter the temperature slightly.
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To make sure that the ball is dropped from the correct height each time.
Predictions
This investigation will depend on a certain amount of potential energy been converted into kinetic (movement) energy. There will be more potential energy as the height of drop increases, because there will be more gravitational potential energy (GPE) converted into kinetic energy; therefore the faster the ball will fall. I took this theory and the calculations for how to work out potential and kinetic energy from ‘Nelson Modular Science,’ (Paul Collison, David Kirkby and Averil MacDonald) on page 202 where it explains this more simply in a diagram of a person falling off a building. At the top of the building, which is 100m high the person has 50 000 J. As the person falls the potential energy is proportionally converted into kinetic energy. Half way down the person has equal potential energy as kinetic energy (25 000 J each). Then just before impact the person has only kinetic energy left as the potential energy has all been converted.
The diagram below shows all of this information in its simplest form.
Using this diagram I can see that:
Gravitational Potential Energy = Kinetic Energy
Using the diagram and the theory, ‘As the height from which the ball is dropped increases, the more potential energy which will be converted into kinetic energy’, I can say that the ball will hit the bench faster; therefore less energy will be transformed to sound and heat and consequently the bounce will be bigger. Accordingly I predict that,
Increase in the height from which the ball is dropped = Increase in the height of bounce
As a result of my prediction I think that my graph will look like this:
Results
This section is mainly based on putting my planning into action, hence all of the practical work and not a lot of written work. The averages in the table are recorded to the nearest cm.
Observations
My results table shows that as the height of the drop increases, so does the average bounce. This is illustrated in the table whereby at 50cm the average bounce height is 36.6cm, and then at 120cm the average bounce height is 75.2cm. If I take away the height of drop from the height of bounce I can see that for each height the energy lost in sound and heat is fairly similar each time the ball is dropped.
I can see from my table on potential and kinetic energy that as the height increases the potential energy increases and as this increases so does the kinetic energy as more energy is been converted.
Analysis
My graph has a straight line of best fit, which suggests that my results are proportional. This means that whatever happens to one factor, it does the same to the other. In my experiment, as I increased the height of the drop, the height of the bounce increased as well; therefore my prediction was correct.
This trend occurred, because the higher the ball was dropped the more potential energy it had. When the ball was dropped the potential energy was converted into kinetic energy and since energy can neither be created or destroyed, only converted it will move at a faster speed; therefore when the ball hit the bench some of the energy was transformed into sound and heat. The energy left after impact and the fact that the upward force is dominating the downward force causes the ball to be forced back up into the air. The more kinetic energy at the bottom, the more can be converted back into potential energy, therefore the ball bounces higher.
There are no obvious anomalous results and there is strong positive correlation between the height of the drop and the height of the bounce, as the points are fairly close to the line of best fit.
Evaluation
My experiment went reasonably well and efficiently, due to the plan that I had drawn up beforehand. I received fairly reliable results from which I drew a firm conclusion. I would not alter the amount of results next time as I managed to gain a maximum outcome in the time selected.
I think that the experiment was fair to some extent, because I controlled all other identified variables and only varied the height. However there were some problems that occurred, which fortunately did not affect the results dramatically; therefore there were no anomalies. I can see from my plan that I conducted a fair test, whereby I used a ruler as a marker each time to help in gaining more reliable results, I repeated the experiment three times and took five readings for each height, I kept the angle of the ruler constant each time, I used the same equipment each time, I kept the mass and the temperature constant each time and I dropped the ball on the same surface each time. The problems that occurred when doing this experiment were those, the ball didn’t bounce in a straight line some of the time; therefore it was difficult to receive good readings. This was most likely to have been caused by the wooden bench being uneven and I could restrict this from occurring next time by using a spirit level. The results could have also been affected slightly, because there could have been a crack on the section of the bench where the ball was dropped. I could varnish the bench next time so that there aren’t going to be any cracks that are liable to affect the results next time. The ruler that I used as a marker was not as efficient as using a light beam or a video camera, because by using a light beam I would have been able to read off the readings more accurately and with a video camera I could record the experiment and then use pause to freeze the picture and then read off the values.
I could extend my investigation further by doing the experiment again, under exactly the same conditions, but this time I would investigate how a different mass of ping-pong ball affects how high it bounces. Even though I haven’t varied the mass in this present experiment, by doing this extended investigation I can determine how mass may be another major factor, which might affect how high a ping-pong ball bounces. Accordingly I can progress further in this area of physics and this will help me in my understanding of this subject.
