PREDICTION
I am able to relate previous scientific knowledge to justify my prediction. I know that when an object is raised to a height it gains Gravitational Potential Energy (GPE) I am also able to prove that the higher the object is raised the greater GPE the object has. I will do so by the use of the following formula,
GPE(J) = Mass(kg)*Gravity(N/KG)*Height(M).
(GPE=MGH)
I will use the formula above to illustrate the GPE gained by an object of the same mass, 0.2kg (200g), same Gravitational value, 10N/KG but dropped from 2 different heights, 1) 1m and 2) ½M (50cm).
1. GPE=MGH
GPE=0.2*10*1
GPE=2 J
- GPE=MGH
GPE=0.2*10*0.5
GPE=1 J
We are able to see that the higher the object is raised the greater GPE it stores. I know when the object is raised it has the GPE according to its position. The ball will also store and loose other sorts of energy, and this will need to be considered for my prediction. I know that when the ball is raised it will have only GPE (1), when it is dropped the ball will gain Kinetic energy (KE) and will start to loose GPE (2) and just before it collides with the surface the ball will have only Kinetic energy (3). Thermal energy and sound energy will be released into the Bench and atmosphere when collision happens (4); the following diagram illustrates this,
When the ball collides with the wooden bench it will gain Elastic Potential energy (EPE). The rubber ball flattens due to the impact of the collision; this is too quick for us to see. Here it gains EPE so the ball is able to ‘bounce’ back up. The following diagram shows the ‘flattening’ of the ball on collision.
I predict that the larger the height of which the ball is dropped the more GPE it will have, therefore the ball will gain KE equal to that of GPE, the impact on the bench will lead to greater EPE and so the ball will bounce up higher.
Results
Before doing the experiment I weighed the ball, it came to a mass of 114.4 grams I will be able to use this when it comes to justifying my results.
The following results table shows the mean height of the bounce. I had time to do a further 3 experiments at each height so there is a total of 6 experiments for each height. The mean of these heights is found and rounded to the nearest whole number.
I am able to see a pattern between the height the ball is dropped and the bounce back height. The height the ball bounces back to is approximately half of the height it is dropped from.
Analysis
I am also able to work out the Gravitational Potential Energy (GPE) the ball gains when lifted to each height, with the use of the following Formula, GPE=MGH, which was discussed earlier in the investigation. The mass of the ball is 0.1114Kg (114.4g) the Gravitational figure is 10N/kg. The information will be displayed in a table format.
By calculating the GPE of the Ball bounced back we will be able to calculate the efficiency of the ball, depending on the out come we will be able to have a rough idea of how much thermal energy and sound energy the ball looses when it collides with the wooden bench, this affects the amount of Elastic Potential energy the ball gains thus affecting the height the ball bounces back to.
We can see that the greater the GPE of the ball when initially raised, the higher the GPE of the ball when it bounces up.
The energy input equals the energy output. We can calculate how much of that energy is used to bounce that ball back up. The following formula shows how,
Efficiency= Useful energy output * 100%
Total Energy input
The efficiency is proportionate to the findings of the heights the balls bounced back to. We know that about 50% of the total energy output is transferred to thermal energy and sound energy on collision.
Evaluation
I predicted earlier that the higher the ball is raised it will gain more GPE and this will transfer to Kinetic energy and when the ball collides with the wooden bench The ball will gain more EPE thus will lead to a larger ‘bounce back’ height.
By calculating the GPE of the balls I investigated I was able to prove that my prediction was correct. By observing the table containing the GPE of the balls at the descending heights we can see that the higher the ball was raised the more GPE it had and so bounced back to a greater height.
The experiment I carried out wasn’t exact and by observing the results and the graph we can see this, we are able to see some anomalous results. This is probably due to my sight it is difficult to see the exact height the ball bounces back up to, that’s why I decided to find the mean average of 6 experiments. If I did more experiments I would be able to pinpoint a more accurate efficiency mark, which should be about 50%. One way of doing this is by placing light gates, which are linked up to a computer they would record the exact height of the ‘Bounce Back’ and would thus lead to accurate results.
The surface the ball was dropped on was wood, it was very uneven and so also affected the height the ball bounced back to, if the surface was totally flat the results would also be more accurate.
If I were to also investigate the ‘bounce back’ heights from when the ball is dropped on different surfaces I would be able to gain a more accurate conclusion.
