Temperature:
In certain balls, there is air trapped inside. When this becomes warm, it expands, and creates more outwards pressure, which effectively, makes the ball harder. When the ball is harder, it will bounce more efficiently. To control this, I will use a ball that doesn’t have air trapped inside.
Drop Height:
I am investigating this factor, I will be varying the drop height. The efficiency of the bouncing ball could change, because although the ball has more gravitational potential energy when the drop height is increased, it also has to travel further through the air, which means that there is more friction to slow it down. However, when the drop height is reduced, the ball doesn’t have a chance to gain enough kinetic energy, to be able to bounce back up as high.
Diagram:
Method:
- Collect the equipment shown in the diagram above, clamp the two metre sticks to the vertical stand, as shown in the diagram. The wall must have a solid surface at its base.
- Drop the rubber ball from in front of the metre sticks at 0.5 metres.
- Record the results.
- Repeat stages 2 and 3, for heights 0.6m, 0.7 m, 0.8m etc, up to 2.0 metres.
Fair Test:
To make sure that this experiment has accurate results, I will repeat the experiment three times, and take an average of the results, to reduce the possibility of any anomalous results.
Safety:
Make sure there is an adult in the room in case any unpredictable accidents occur such as:
The ball ricocheting of the table at a peculiar angle and goes in your mouth and makes you choke.
Make sure you wear goggles and body amour in case an armed robber invades the classroom and decides to shoot you for fun, or a little fairy man jumps on your back and tries to stab you with a 4 inch poison dagger!
Prediction:
In this experiment, the ball will bounce higher, as the drop height increases. This is because the ball has gained more gravitational potential energy, to be transferred into kinetic energy, but the ball will lose more energy when it bounces, because there is more of a force pulling it downwards, and forcing it to change shape. As it is stated in the laws of conservation of energy, the kinetic energy is not lost, but transferred into less useful forms of energy. As the drop height is doubled, the bounce height will also double, but it will become less efficient.
Preliminary Work:
For my preliminary work, I tried out the experiment that I was going to do to investigate the effects of the drop height on the efficiency of a bouncing ball. I only repeated the results twice, which I will increase on my true experiment to three times. This is because, I felt that the results could be more accurate. I also chose to take a wider range of readings. In the preliminary work, I used various drop heights, between 0.5, and 1.4 metres. I have now changed this to heights between 0.5, and 2.0 metres.
Preliminary experiment:
Results:
To work out the efficiency, I used the formula;
EFFICIENCY = POWER OUT
POWER IN
I found the POWER IN, with this formula;
POWER IN = GRAVITATIONAL POTENTIAL
GRAVITATIONAL POTENTIAL = MASS x g x Height
Mass = 72 g g = 10 Height = ?
GRAVITATIONAL POTENTIAL = 72 x 10 x HEIGHT
GRAVITATIONAL POTENTIAL = 720 x HEIGHT
e.g. drop height = 0.5
power in = 720 x 0.5 =360
The power out is found by multiplying the average bounce height by the gravitational potential.
e.g. Bounce height = 0.33
power out = 0.33 x 720 = 237.6
so;
EFFICIENCY = 237.6
360 x 100
Analysis
From the results of this experiment, we can see that the ball becomes less efficient, as the drop height increases. This is because the ball changes shape, and ‘uses’ some of the energy. Because some of the energy is being lost, it means that the transfer of energy is less efficient, so the bouncing of the ball is less efficient. This means that my prediction was correct. The graph also shows that the balls efficiency changes, and it becomes less efficient.
Evaluation
I think that this experiment went very well. The method worked well, and the results were better than expected. To improve the accuracy of the recordings, the bounce could be recorded on a video recorder, so that it could be played back in slow motion, and paused if necessary, so that you can see exactly how high the ball bounced. There were only a few anomalous results, which can be seen on my graph. I don’t think that I would benefit from taking any more results, if I were to do this experiment again. I think that it worked well, and the method wouldn’t need changing. However, to make it easier to record the results, I would set up a video recorder, as shown in the diagram below. This should make sure that the results are accurate, as it could be played back as many times as possible, to reduce the possibility of human error. This could account for some of the anomalous results (shown on the graph).
