If a ball were completely efficient, no energy would be lost during the bouncing process. For this to happen, no energy can be lost with sound or thermal energy due to friction. If a ball lost none of this energy whilst being dropped and hitting the floor, it would bounce to the same height as it was dropped from. The ball needed a certain amount of kinetic energy to move from the height it was dropped from to the surface it hit. If the ball were completely efficient, it would still have exactly that same amount of energy needed to move it the same distance back to where it was dropped. No ball can do this however; some balls are more efficient at not losing energy than others.
When a ball is dropped it mainly transfers two types of energy, but also uses and wastes others. These are:
- Gravitational potential energy
- Kinetic energy
- Elastic potential energy
- Sound energy (wasted)
- Thermal energy (wasted)
Gravitational potential energy and kinetic energy can be worked out by these formulae. I will be using these later in my experiment:
Gpe= weight (n) x change in height (m)
Ke= 1/2mv2
=1/2 x mass x velocity2
When the ball is dropped, the gpe will transfer into ke because rubber is a dense material and its particles are held together by covalent bonds. This is when two atoms electrons are being shared by the two atoms. These electrons spend their time between the nuclei, screening their positives charges, therefore allowing the nuclei to come closer together than if the electrons were not there. However it is the negative charges from these electrons that attracts both nuclei and holds them together in a bond. When the ball heats up it will give these bonds more thermal energy, which will be transferred to create more kinetic energy for the ball.
Prediction
I think that the efficiency of the ball will change as the height you drop it from increases, because as you increase the height, the ball will bounce higher because there will be a greater amount of Gravitational potential energy for it to transfer into to kinetic energy. Also the velocity of the ball will increase as the height the ball is dropped from increases and this could affect the efficiency because the ball or floor or both may need to use more energy to return to their original shape if they get dented.
Method
There are two ways in which I could do this experiment, hold the meter stick from the table or floor. I have chosen the floor.
Here is a list of things I will need to do before I tart my test:
- I will have to measure the weight of the ball so I have the mass for doing my equations.
- I will need to make sure I have the following: 1 metre ruler, 1 ball, Scales, Table of results.
- I will need to make sure that the method I will use will be a fair test.
To do the experiment I will need to:
- Weight the ball and note down for use later in equations.
- set up the experiment like so:
- Start by dropping the ball from 1m (100cm) high and measure hen the ball bounces back to, and record this on your table of results
- Repeat the test going down in 10’s until you get to 10cm, recording the values as you go.
- Draw a graph with your results and repeat any anomalies that have occurred.
Fair testing
To make this a fair test I will have to consider the factors that could affect it and find a way to overcome this problem.
Pre-test
You conduct a pre test to see if what you are trying to find out is worth testing. Whilst doing the pre-test you are likely to find something wrong with your experiment and will need adapting, to ensure you get the best results.
Results table and graph
My pre-test graph shows many anomalies. These are probably caused by not reading were the ball bounced to correctly. In my actual test I will have to drop the ball more than once to get an accurate reading. I have repeated this test to see if I could get a more accurate reading but it sill has anomalies.
This graph was much straighter but there are still a few anomalies.
Pre-test conclusion
As the height the ball is dropped form increases the height it bounces to increases. This could suggest that as the height you drop the ball from increases so will the efficiency, which is exactly what I said in my prediction.
Experiment
I have followed my method again with an added change which was to repeat the drop more than once to get an accurate result, and this is what I have got:
This graph shows the results of my experiment. As you can see I have achieved much better results in this than in my pre-test. This still works with my prediction and I will be able to prove this better when I do my equations. By looking at the graph I can see that starting from the first result which is 2, it goes up by 6 every time. This may relate to how much the efficiency goes up as well.
I have only worked out a selection of values to see if I could notice a pattern in the results. However I have not noticed anything and if I carried on with the values I don’t think that I will.
Conclusion
As I said in my prediction the efficiency of the ball will change as the height you drop it from increases, because as you increase the height, the ball will bounce higher because there will be a greater amount of Gravitational potential energy for it to transfer into to kinetic energy. Also the velocity of the ball will increase as the height the ball is dropped from increases.
In my pre-test I gained a lot of anomalous results, and when I redid this test I can pout with the same number of anomalies, some in the same places. I think these were all caused by human error, as I was hard to see where the ball bounced back to. This could be improved by dropping the ball two or more times to get a more accurate result.
In my main test, my results came out much better with only one anomaly that was only out by a centimetre or two and both tests coincided with my prediction.
In conclusion I can see that as the height a ball is dropped from increases so does the efficiency. This is what I said in my prediction. I can prove this by looking at my table of results and the efficiency graph. I can see no patterns between the results. I think this has happened because the weight always stays the same and it is only the height that changes the ball will have more gpe to transfer in ke.
Evaluation
Overall, I think that my results were as accurate and reliable as I could make them with t he equipment I was provided with. I don't think that seeing how far a ball bounces alongside a ruler and getting a person to measure the bounce is a very accurate or reliable way of carrying out the experiment. There is too much
risk of human or experimental error. The ball could have been dropped by mechanical means to make sure that no force was exerted on it. Once my one anomalous result had been excluded on my actual experiment, all my results did fit the line of best fit quite closely, which helps to prove that my results are reliable. My anomalous result was probably due to experimental error e.g. slow reaction times etc.
If I could extend this experiment even further, I think I would carry out the same experiment with a different ball. This way, I could relate the results I have gained with a tennis ball with results with say a ping-pong ball. The pressure inside a tennis ball is different to that of a ping-pong ball. It would be interesting to see what difference this makes to the results. Also, the tennis ball is made of a different material and is squashy. A tennis ball has a bigger surface area than a ping-pong ball because it is bigger. I predict that air resistance has more effect on a tennis ball than it does on a ping-pong ball. Therefore I predict that the graph will look very similar in direction, but the graph for the tennis ball will be a steeper line than the ping-pong ball will have. This is because the tennis ball will be losing more energy due to air resistance. However the ping-pong ball may result in a curved graph because a ping-pong ball is a tight structure and doesn’t sag at all or squash as much this means that it is highly pressurized in the middle. Therefore when the ping-pong ball hits the ground, it doesn’t need to be dented as much as other balls to release the same amount of potential energy needed for the bounce.