Preliminary experiment
Planning:
I will for this experiment investigate the factors which can affect how the ball bounces. The factor in which I will be investigating is the height at which the ball is dropped. I have chosen to vary this factor because it is easier and quicker to construct within the time constraints I had.
Before doing my final experiment I will be constructing a few preliminary experiments to help me understand more about the range of readings I should use, the surface of which the ball lands on, and how the readings should be recorded i.e. by using a video camera, taking snapshots etc.
Preliminary experiments can help me produce a more reliable set of results for my final investigation, as I would have realised and corrected the mistakes I made, helping me to plan for a better investigation the next time.
As the variable of the experiment is the height at which the ball is dropped, I will be altering the height of the ball using a metre ruler. The measurements will be recorded by human eye level (me), since we couldn’t find a camcorder. Further planning of the final experiment will be displayed after the preliminary experiment.
(People I worked with during the investigation are: Leah and Maan.)
Since we are recording the measurements from human eyesight, it would be hard to get an exact reading the first time; therefore we have come to the conclusion of dropping the ball three times before recording the final results. Here is how we did it:
- First drop: to get a rough idea of the height range at which the ball bounces back, the person measuring it will therefore know where to focus on the meter ruler.
- Second drop: to get a rough estimate of the bounce.
- Third drop: to confirm the height at which the ball bounced back and recorded this measurement in the table.
The measurements for the first two steps are not recorded because it was just a rough guide for recording the final measurement. Nevertheless, I have found out after the experiment that the guide measurements are similar to that of the final measurements recorded in the table.
Before carrying out the preliminary experiment we experimented dropping the ball from each height range, every 10cm (without recording the measurements). We have found that dropping the ball from the 0 cm and 10 cm proved to be difficult as it was hard to reach to a decision of the height at which the ball bounced back. Therefore for our preliminary experiment we started our height range at 20 cm due to eye level difficulties of getting a reading at 0 cm and 10 cm.
The experiment was carried out on a bench to get a better view of the readings, from eye level. The surface at which the ball landed on was wood, which is also the material of the bench.
A tennis ball was used to carry out the experiment.
Table of results:
Graph: the average height at which the ball bounced back (cm)
Evaluation:
I have realised after the experiment that by changing the person recording the measurements can affect the reliability of the results as it is not fair testing. We originally exchanged the person recording the results because we thought that we could get a different opinion on the results, but later we realised that different people have different brain reactions towards measuring the ball therefore the results might vary. We also noticed that people might have different ways of judging the height at which the ball bounces back i.e. one person might measure the height of the ball from the bottom, whilst the other might measure the height from the top of the ball. In this case we recorded the height from the bottom of the ball because the ball was dropped with its bottom touching the measurements. (See diagrams below)
As a result of this experiment we have come to the conclusion that for the final experiment we would have to have the same person recording the measurements, and that person will be me.
Final Experiment
Planning:
For the final experiment I have decided to still use the method from the preliminary experiment but make sure that it is the same person measuring the bounce of the ball. I will use the same ball throughout the whole of the experiment to ensure it is a fair test. I will still use the wooden table as the landing surface of the ball, because from the preliminary experiment I found that the table was the most appropriate surface for the ball to bounce on as it gave us a better eye view of the bounce and it also have similar properties as the other surfaces.
Prediction:
I predict that the height at which the ball bounce back will be half of the height at which the ball was dropped. This is proven in my preliminary experiment (see graph on pg 5), as the graph proved to be proportional since it produced a straight line. It is also seen in the table that the average bounce of the ball is half to the height it was dropped.
I predict that the bounce of the ball is only half the height at which it was dropped because half of its energy has been low-graded by heat and sound. As a result the ball only has half of its useful energy to make the ball bounce back.
However, as the height of the ball increases so would its bounce. This is caused by the atoms in the ball vibrating, as the ball is hits the table. The higher the distance the greater the force will act upon the ball (weight of ball plus distance travelled) causing it to hit very hard onto the surface. This force is then enough to heat the ball causing the particles inside the ball to vibrate and therefore bounce higher.
Fair testing:
- Using the same ball from the preliminary experiment so the height at which the ball bounces back won’t vary.
- Make sure that the ball lands on the same surface, wooden table, and that the surface is flat, no angles. This is vital as it can alter the height at which the ball bounces back.
- The temperature of the ball must remain roughly the same during the experiment as an increase or decrease in temperature can also affect the height at which the ball bounces back.
- The way the ball is dropped must remain the same (see page 5), whether force is added when the ball is dropped or not.
Apparatus:
- Metre ruler
- Tennis ball
- Wooden table
Method:
- Hold the ball at the height in which you are going to measure e.g. 20 cm.
- Drop the ball and get a rough idea of the height range at which the ball bounces back.
- Drop the ball again to get a rough estimate of the measurements at which the ball bounces back.
- Drop the ball for the last time to confirm the height at which the ball bounced back and recorded this measurement.
- Repeat all the above steps for the next height range at which you are going to measure.
N.B. to save less hassles in measuring the bounce, it would be ideal to have three people constructing the experiment. One to hole the ruler, one to drop the ball and one to measure the bounce.
Diagram:
Results:
Graph: average height of bounce (cm)
Analysis of results:
My results illustrate the height at which the ball bounces when the height dropped has been altered. By looking at my graph I was able to determine the relationship between the two factors. As the drop height of the ball increases so does the height at which the ball bounces back. This is identified in my results, as the graph proved to be proportional, in other words the height at which the ball is dropped is proportional to the height at which the ball bounces back.
Although I did not drop the ball at the height 0cm, I am certain that its bounce will also be 0cm because the ball was not lifted therefore it rests on the table and usually the downward force of an object on the table will equal to the upwards force of the table on the object . As a result the ball will not bounce because there is no friction. Since there will be no bounce of the ball at the height of 0cm it is fair to suggest that the graph will have a straight line through the origin which makes it a proportional graph.
From the graph I was also able to find out that the height of bounce was ½ of the original height of each drop. This was worked out from the gradient on the graph.
Gradient= Y / X = 16cm / 32cm = 0.5
The bounce of the ball is only half of the height dropped because a lot of its energy is wasted on friction of when the ball hits the table, these wasteful energies involves heat and sound. This was explained in my prediction, having worked out the gradient of the graph I could conclude that my hypotenuse of the ball bouncing back at half of the height it was dropped was right.
There are many stages of energy transfer in the process of the bouncing ball. Here is what I concluded: -
Gravitational potential energy -> kinetic energy -> elastic energy -> heat & sound energy -> repeat of cycle. Refer to background science for further details.
Evaluation:
Having examined my results, I feel that there are areas in the experiment could be improved to produce an even more accurate and reliable set of results.
First of all the range of readings recorded was very limited and I feel that the range is not enough to consider the results to be reliable, even though we planned to start the range at 20cm as we found the measurements easier to record. Enable to improve the reliability of the results we could have recorded a wider range of readings, from 0cm to perhaps 200cm this will then give me a wider range of readings to examine and compare with. However, repeats were carried out in the experiment to confirm that the readings were accurate, and from this aspect I suppose the results I recorded were quite accurate but more is needed to make it reliable. Having starting the range at 0cm will prove that the graph will go through the origin instead of just making an assumption on it.
In some areas human errors were made, this is expressed on the graph; there were a few anomalous results. The errors might occurred due to the reaction speed of the person recording the measurements or it might have been that the ruler wasn’t kept upright during the experiment causing a slight variation in the measurements recorded. There are ways to avoid or improve these errors i.e. using a camcorder to record the height of the bounce instead of human eye vision, this way the tape could be played back in slow motion, increasing the accuracy of the results.
If I were given more time, I would extend the investigation focusing on other factors, which would affect how a ball bounces. Varying the temperature might be an interesting factor as I would like to find out the freezing and melting points at which the atoms in the ball are affected, but this might depend on the material of the ball.
Bibliography:
Textbook: Physics for you
C.D Rom: Letts GCSE - physics revision
