Air resistance – this force will be counter acting against the ball, as the air molecules hit the ball the effect will be that the ball slows down, resulted by the loss of kinetic energy meaning that the ball will not bounce as high as it was dropped.
Heat – if the temperature is very high from the loss of body heat or the air temperature, it causes the molecules to move around inside the ball. This movement makes the ball’s material more turgid and means that it won’t lose as much elastic potential energy when it hit the surface. This results in a higher bounce height than if the ball is cold.
I am hoping that the air resistance will balance out the heat transferred from my hand and mean that my results are reliable.
My Prediction:
I predict that in this experiment my results will show that the bounce height will be directly proportional to the height it is dropped from; and that all the experiments will show an equal percentage loss of energy. During the experiment there will be several exchanges of energy, firstly the ball will hold gravitational potential energy before it is dropped. Then while it travelling through the air the energy will have transferred to kinetic energy. The ball squashes because it is hollow; the more it squashes the more energy- in the form of heat- it loses, thus when it is squashed it stores energy as strain/elastic potential energy. This means that it can bounce back. Although, the higher you drop the ball from the more speed it can pick up, this means it hits the surface with more force, hence meaning it squashes more and loses more energy. From this I predict that as I drop the balls from higher measurements, the height the ball bounces back will relate equally. As a result, if I drop the ball from 50cm, then from 100cm, the re-bounce of the ball should be double from the one before. This is because, for example if the ball I drop from 50cm bounces 35cm back, it has lost 30% of its energy. Then the other ball I drop from 100cm bounces 70cm back, it has also lost 30% of its energy. I think this will happen because the higher I drop the ball from, the more force it obtains; therefore when it bounces it will lose more elastic/ strain energy and not bounce considerably higher, but bounce in relation to how high I dropped it. This means the graph should look like this:
Moreover, I believe that due to the weight of the ball, and air resistance acting against it, the idea of terminal velocity will affect the speed of the balls downfall. I think that the two forces will balance each other out therefore the object will not be affected by the air resistance because of the weight.
However, I know that there will some human error in this experiment that is impossible to stop. Firstly, it will be difficult to judge the height the ball bounces back, but to overcome this as much as possible, I will stand in the exact same place for each experiment and read the measure from the bottom of the ball at eyelevel. Moreover, I cannot be certain that when I drop the ball I will not exert some force. Therefore I will always drop the ball so if I do then the force should be equal, and I will hold the ball between my finger and thumb to overthrow this as much as possible.
To sum up, I believe my results will show that the height I drop a ball from is directly proportional to the height it bounces back, and that the percentage energy loses will be equal for all the experiments from different heights.
My Results:
Analysis:
As the results and the graph attached overleaf shows, the line of best fit indicates that my prediction was correct, although due to experimental error it is not exact. However, as the end column displaying the percentage loses shows, although the percentage losses vary they are all around the same point. I think air resistance did have an affect and slow the ball down, this meant it was unable to pick up a lot of speed, meaning it didn’t have much kinetic energy and what it did have was lost when it was still for a split second as it squashed; released more energy in the form of heat. Therefore the percentage loss increases near the end as the drop height increases. I think that my prediction about the percentage loss was right because the end column shows no big anomalies, which means that the ball was constantly losing the same amount of energy wherever I drop the ball. This indicates that the air resistance did not have as bid affect as I thought.
Towards the end of my experiment, the graph shows a clear place where a factor influenced my results. The last three points are some what away form the trend of the rest; this could be because I had reached a point where terminal velocity concluded. I think this because they are significantly lower than the rest of the points. This leads me to believe that air resistance had an affect of the bounce height due to terminal velocity no longer being in control. These last results are anomalies as they do not follow the trend of the rest, and are notably away from the line of best fit. I would expect to get a result of approximately 22 when dropping from one metre; however I actually got about 21.5. consequently, I believe
Moreover, I expected that if I dropped it from 100cm it would be double that of the bounce from 50cm. This was incorrect, as 12.3 x 2 does not equal 20.407. I believe this was because in this case air resistance did have an affect, or the heat I expected to transfer from my hand did not, maybe due to it me doing the experiment in the middle of winter.
On the other hand, in my prediction I stated that the bounce height would increase as the drop height increases, and the straight line defiantly shows this. In my opinion, at the end of the graph, the gradient increases causing a steeper end to the graph. This is probably because I did these heights at the end of the experiment, therefore the ball will have had time to warm up, causing the molecules inside to move around and make the outer edge of the ball harder, meaning it bounces higher.
I believe that my graph does not have a very steep gradient due to that when I drop the ball higher; the friction against the air coincidently increased.
I decided to draw my graph from the origin point, as that is the only point of the graph that is free of experimental error, as you can’t drop a ball from nothing and expect it to bounce, as it has no GPE.
Evaluation:
Overall, I do not think this experiment was very reliable, as there were so many factors that were out of my control to manage. These were such things as the air temperature, the air resistance, heat, and the pressure inside the ball. The air temperature could have affected the activity of the molecules inside the ball, and brought into action the Kinetic theory. The kinetic theory is that of the molecules gaining more energy and exerting it on moving around, consequently colliding with each other and making the ball harder due to the increase in the pressure. This may have made the ball bounce harder as it got hotter through the experiment. Although I said pressure would be one of my controls, I did not take into account the pressure building up due to the heat transferred. Moreover, I could not control the air resistance, although this should have stayed constant, I can’t be sure. If the air temperature increased through the experiment, maybe because of the body heat given off, it would mean that the air resistance increased. This is because the heat gives the molecules energy, so the ball would have to use more energy to push past them. This energy is then lost, and means that the ball does not have as much energy as it would if it were cooler. Furthermore, I think because we used our eyesight to determine the height of the re-bounce, this made our results even more unreliable.
Yet, on-the-other-hand, I also think my results were as reliable as could I could get them. This is due to the limited time and equipment. For instance, because we used a clamp and stand to hold up the ruler, it made the results trustworthier than someone holding it up. Also, the only thing we varied was the height we dropped the ball, everything else was kept exactly the same, for example, the ball we used, and the surface we worked on. What’s more, I followed the procedure correctly and missed nothing out. I measured the height of the re-bounce from the bottom of the ball instead of the top, as when we dropped it the bottom was inline with the top of the ruler. Moreover, because I got an average, it reduced the affect of anomalous results, which meant my result are unlikely to be flawed due to me as the dropper.
I do not think the way I measured the height was very accurate, as it depends on individual eyesight, and everyone’s level of eyesight is different. Although, they way I dropped the ball, and how we went about trying to record the closest measurement was accurate. This is because I used only my finger and thumb to hold the ball, this was to pass as little heat over as possible, and stop dropping the ball with an added force. I believe this worked, as on my graph there are no obvious anomalies, the line is not straight, but that is due to only a small bit of experimental error.
If I repeated the experiment there would be lots of things that I would do differently. I would conduct the experiment on the floor instead of on the bench, as maybe the increase G.P.E on the bench influenced my results. Also, I would find some way of controlling the air temperature, and the air resistance, although this would have to be done outside of the lab. I think that the temperature and the air resistance did have an effect on my results as the percentage of energy lost increased as I dropped the ball from higher positions. Moreover, I would find a way to measure the level of the re-bounce that would be more dependable than using my own eyesight. This is because, as I have said, eyesight is not consistent as things such as the light intensity, which may affect the recording of the results, can influence it. Furthermore, I would increase my drop heights to 200cm, as I think if I carried on longer, my graph would show a definite point where terminal velocity came into action, and also that that graph would perhaps increase its gradient as the ball got hotter through the experiment. This would be useful as it would mean my results could be analysed further and draw a conclusion more valid.
Although, if I did do the investigation again, I would keep the squash ball in my experiments. I believe it gave reliable results subject to the terms and conditions that applied freely. Also, I would use the same unit of measurements, as they showed the results clearly and were more appropriate than other methods.
I could repeat the experiment under converse conditions by for instance changing the surface, or the air temperature. I could also vary the ball I used, as this would allow me to compare different bounce heights from the same drop height. This would mean I could calculate the efficiency of the balls I used. What’s more I could change how I measure the height it bounces back, or actually what I measure. I could measure the efficiency of the ball, and how the height I drop it from affects the amount of energy is lost.
