Squash ball: I will be using a regular squash ball with a diameter of 4 cm
Stop watch: I will also be timing how long it takes from the ball to hit the floor in order to have all the factors to work out the velocity of the ball.
Weighing Machine: to find out the mass of the ball.
The variables I intent to keep the same are the temperature, the ball, the surface.
The factor I will alter each time is the height from which the ball is dropped.
How a squash ball would look if it were cut in half
Diagram:
Energy Transfers
Firstly, to pick up the ball myself I will be using chemical energy from my body. When I am holding the ball ready to be dropped it will have gravitational potential energy (GPE). Once it has been dropped, this energy will be transferred into kinetic energy while it is falling. When it hits the table the ball is squashed into a more of an oval shape. At this point, the kinetic energy is transferred back into GPE and some will be transferred into heat. This is reason why the efficiency is never 100% and the ball never bounces back to its original height is because of the wasted heat energy. When it is in this oval shape it is like a spring, ready to release the energy back into kinetic once again and it bounces up into the air.
GPE Kinetic GPE & Heat Kinetic
The one factor that I will be changing is the height of which the ball is initially dropped.
I will be dropping the ball from the side of a ruler to make sure the height is accurate. The heights of which I will be dropping the ball from are: 100, 90, 80, 70, 60, 50, 40, 30, 20, and 10 cms. I will then watch the ball as it falls and record how high the bounce is. I will also be timing how long it takes for the ball to hit the floor from the drop height. I will do this using a stop watch. I will be doing each height 3 times and then working out the average to make sure my results are as reliable as possible. I will be recording the bounce height in one decimal place and the time in milliseconds to make sure my results are as accurate as possible. I will also make sure that the table is at eye level when I record the bounce height to avoid parallax error.
Once I have obtained my results I will be working out the average of the drop height and time using the following formulas:
Drop height average:
d1 + d2+ d3
3
Time to drop average:
t1 + t2 + t3
3
d = drop height
t = time
123 = first, second and third result
I will be dividing them all by three because I am doing each drop 3 times.
I will also be working out the efficiency of the bounce. I will do this by using the following formula:
Average Bounce = Efficiency
Drop Height
I will also be working out the speed of which the ball is falling, this is the reason I am recording the time as well as the bounce height. To work out the speed of the ball I will be using the following formula:
Distance = Speed
Time
As I have stated earlier I predict that the height from which the ball is dropped the higher the ball will bounce. Here is a simple sketch of what I predict the graph to look like:
I predict that the higher the drop height the higher the ball will bounce because the higher it is dropped the more GPE it will have. Then once it is dropped the greater the speed it will reach because the GPE will have transferred into kinetic energy as I have mentioned earlier. I higher the amount of kinetic energy it hits the wooden table with the more of which will be transferred into GPE again and then subsequently, the more that will be transferred back into kinetic energy once again. Therefore the higher the ball will bounce.
Results
Analysis
Bounce Height Graph
From this graph I can see that there is a positive correlation between the two factors, drop height and bounce height. It is almost exactly like the sample graph I drew earlier. There are no anomalies and the points are almost in a straight line.
From the line of best fit and the directions of the points I can tell that if I had went higher in the drop height the bounce height would also increase accordingly.
Efficiency Graph
From this graph I can see there is a negative correlation between efficiency and drop height. It seems as if the higher a ball is dropped from the lower its efficiency. This is because the higher it is dropped, the more impact it has when it hits the table. This will cause the ball to be more squashed then if I had dropped the ball from a lower distance. The more squashed the ball is the more energy that will be transferred as heat, and therefore the lower its efficacy.
Therefore is I throw a ball at a wall with a lot of energy, I would expect the ball to not bounce back very far.
Again, for the line of best fit and the direction of the points I can tell that if I had went higher in the drop height the efficiency would have sunk even lower.
How my results compare with my prediction
My results agree with my prediction. The higher the ball is dropped from the higher the bounce height.
Speed
Firstly using the time and distance I will work out the average speed on which the squash ball was falling.
Speed (m/s) Distance (m)
Time (s)
There does not seem to be any correlation or relationship between drop height and speed.
Evaluation
I believe my sets of results are reliable because I have controlled all the variables that could effect the investigation and there were no anomalies. However, I believe there are some areas where it could have been improved.
Firstly, I feel that that I could have measured the bounce height and the time taken for the ball to drop. Although I was at eye level with the table I think that an electronic device such as a camera could have given me a more reliable answer for the bounce height. As for the time taken for the ball to drop I feel that near the end when I was dropping the ball from much smaller height the time was harder to measure as the ball was hitting the table so fast, so the results near the smaller distance may not be as accurate, although they do fit in with the line of best fit.
I only had a small anomaly on my efficiency graph where a drop was more efficient being dropped from a higher height than a lower one.
Further Work
I feel that further work would give me additional relevant evidence.
Firstly, I would like to try higher heights to see how inefficient the bounce could get. Also, if it were possible, I would like to measure the heat being given off from the ball when it hits the table.
Conclusion
Overall, I think that I effectively achieved my aim. I believe I used my scientific knowledge to explain my results and analyse them. My investigation successfully proves that drop height affects the height of the bounce of a squash ball.
