Prediction:
In this investigation I will investigate the percentage energy loss when a ball bounces. The variables that could affect the amount of energy lost are:
- The height the ball is dropped from.
- The type of ball used
- The size of the ball
- The temperature of the ball.
- The type of surface the ball is dropped on.
The height the ball is dropped from will affect the energy lost because the higher the ball is dropped from the more force it will it the surface with, and therefore the more power it will lose through sound, vibrations, and heat.
The type of ball I use will effect my results, because some balls will have more elasticity than others, causing them to bounce higher. Also, balls will have different levels of pressure inside them. The higher pressure is the higher the speed of the molecules. When the molecules go at a higher speed they will have more kinetic energy, so the molecules will hit the walls with a greater frequency and force, and so the pressure on the walls will increase. This will make the ball bounce higher because it will hold more energy.
The size of the balls will effect my results because Force=Pressure x Area so a change in area would also cause a change in force.
The temperature of the ball will effect my results because if there is a higher temperature then the molecules will move at a greater speed and the ball will have more energy causing it to bounce higher.
The surface I drop my ball onto will effect the amount of energy lost because some surfaces, like softer surface, will absorb more energy and cause the ball not to bounce up as high.
To ensure a fair test I will choose one variable to change, and keep the others constant throughout the investigation. There are other variables that could effect the outcome of my investigation, for example gravity. However, gravity is always constant on the earth, and is a force of about 9.8 m/s2. This would be too hard for me to change in a classroom situation. I will also not exert any force on the ball other than those already acting on it, because it would be to hard to keep the force constant, and would mean the test was not fair.
For this investigation I will only change the height the ball is dropped from. I have chosen to use the height because, although all the variables are hard to accurately measure, height is easier than the others. Height is also a constant variable (unlike, type of ball or type of surface dropped on), which will help me when recording my results. Using a variable that I can measure fairly accurately will help ensure a fair test.
By investigating the percentage of energy lost when I drop the balls from different heights, I will be able to see if there is a relationship between bounce height and drop height. This is also the relationship between potential energy and kinetic energy.
Because some of the energy will be transferred into non-useful energy, mainly heat and sound, I do no think the ball will bounce up to the same height as it is dropped from. I think that the percentage of energy lost will remain approximately the same no matter what height I drop the ball from. This is because the amount of energy lost to non-useful energy such as heat and sound is proportional to the gravitational potential energy the ball has to start with.
Method:
I will drop my balls from various heights up to a meter. (The Heights I will use will be: 40cm, 60cm, 80cm and 100cm) I will then record how high they bounce up on the next bounce. I will do each experiment 3 times and take an average to ensure I have accurate results. I will time all my experiments using a stopwatch.
I learnt in my preliminary work, that if I drop a ball from lower than 40cm it is very hard to measure the bounce height. This is why I have left out the bottom height which would have been 20cm.
I will try and drop the balls straight downwards because this will make it easier when I measure the height they bounce up to, as I wont have to move the ruler too much. This will also ensure a fair test, as my results will be more accurate if I am not moving the meter rule, as moving it could mean it is not entirely straight and would cause me to take an inaccurate measurement.
I will not exert any force on the balls as I drop then, because it would be virtually impossible to keep the force constant, and would therefore make my results unreliable.
I will calculate how much energy my balls have using the equation PE = mgh, this will be PE1. I will then drop my ball and record the height it bounces up to. I will then record its potential energy, again using the formula PE = mgh, this will be PE2.
I will then find the percentage of energy they have lost using the formula:
PE2 x 100
PE1
Diagram:
