1 meter ruler stick – I chose this because it was more accessible and something else like a tape measure would not be reliable as it is not solid and can move more easily. I will use this to measure the bounce of my ball. 1 squash ball – I am using this because it was available and has a smooth round edge so it will bounce straight back upwards. This will be the ball I use in the experiment. 1 stand and clamp – I have chosen this so that it can hold up the ruler straight and not move it around like a person would. This will hold up the ruler straight.
Diagram -Preliminary work has shown that the squash ball gives more reliable results compared to other types of balls, and works best on a hard surface. I plan to measure the re-bounce of a squash wall when dropped vertically from various heights; this will show me the how the height a ball bounces depends on its drop height. I will do this by using the planned procedure below: Method – ? Firstly, set up the apparatus, ensuring that the ruler is perfectly straight and that it is the right way up – 0-100 from the bottom of the surface. ? drop the ball from the first point and record the height the ball bounces back up to.
? repeat this till all the desired dropping points have been covered. ? To ensure that it is a fair test, repeat all the experiments 3 times to enable us to get an average and consequently reduce the affect of anomalous results on the overall result. To confirm that all the results are fair I gathered an average by repeating the same experiment three times and recording the average. Also, I made sure that each time I dropped the ball it was lined up correctly and that I measured the re-bounce from the bottom of the ball not the top.
So that the ball bounced straight upwards I worked on a smooth bench surface, also because the bench is hard it means the ball will have better elastic potential energy. What’s more, we have used the exact same ball throughout the experiment, as using a different ball with a different density would mean that the one that was less dense would squash more, as that particles can be compressed further than a ball made of high density material. Furthermore, I know that gravity will be constant in this experiment as it is out of my power to change.
Also, I will not vary the angle of the bench or the angle I drop the ball from. The bench will remain horizontal, and I will drop the ball perpendicular to the bench. My independent variable will be the various heights I drop my ball from, causing my dependant variable to be the height it bounces back. My controls are that I will always use the same ball, with the same material and pressure inside, and work on the same workbench. In this experiment there are two things that will affect my results:
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: Height of drop cm 1st recording 2nd recording 3rd recording Average Approx. % of energy lost .