Repeat readings will be done so an average can be taken. This will make the results more reliable and the average more accurate. Three different tests will be done at each temperature.
The measurement of the bounce will be taken to the nearest cm. To read the length accurately, the person taking the reading will be looking at eye level. The bounce will be measured from the bottom of the ball.
A diagram to show the set out of apparatus in the experiment
The equipment used will be
-
a squash ball
- a metre ruler
- a beaker of water
- a kettle
- ice
- a clamp stand
- a polished wooden table top surface
I already know that when you deform an object it will go back to its normal form until it reaches its elastic limit. When the ball is dropped it will deform as it hits the table top
I predict that the hotter the squash ball the further it will bounce. This is because the squash ball is hollow and therefore contains air. The air will be able to store some potential energy from when the ball is in the air, which will change into kinetic energy when it hits the ground to bounce back. If the balls are hotter the particles inside the ball will gain more kinetic energy, so the pressure inside the balls will increase. The hotter the ball the less it will deform this will make the ball hard and so they will bounce higher. It will deform less because there will be more pressure acting on the ball from the air inside it. This is proven by the Pressure Law which states that ‘For a fixed mass of gas, at constant volume, pressure is directly proportional to the absolute temperature’. Therefore as the volume is staying the same, the higher the temperature the higher the pressure.
The balls potential energy can be calculated by this equation:
Potential Energy = Mass x Gravity x Height
The mass of the squash ball is 24 grams, the gravity 10 and the height 100. Therefore the squash ball’s potential energy is 24000 J, or 24 kJ.
If the ball bounces back at 10% of its original height than 90% of it’s energy must have been lost by heat.
By bouncing the ball it will deform as it reaches the surface but it will got back to its normal form until it passes its elastic limit when it will lose the energy as heat. Energy will also be lost by breaking bonds, as heat. This will result in not all the energy being used to increase the height of the bounce.
Obtaining your evidence
The experiment was carried out very accurately following the plan. Accuracy was taken into great consideration to get the best results. The thermometer read the temperature of all the water, as it was being stirred, and the squash ball being left in the water for 5 minutes so it could adjust to that temperature each time.
This is a table to show the results of my experiment
This is a table to show the results from this experiment (from the average) in comparison to the results of another group and the results from a computer program with this experiment on it.
Analysis
From the graph showing the results from this experiment it can clearly be seen that the higher the temperature of the squash ball the higher the height of bounce, agreeing with the prediction. This is shown in every case. In the graph the results did not fit exactly on a curve of a straight line but they did show a clear positive correlation.
Looking at the results from Will’s experiment they also follow a clear positive correlation agreeing with the prediction. The results from the computer also do this but they also fit on a clearly defined curve. The computer’s results also reach a higher bounce height, this maybe because the computer programme had a different weight or diameter squash ball or used a different type of rubber.
Overall it can be seen that these results agree with the prediction that the hotter the temperature of a squash the higher it will bounce. This is because the heat from the water gave the particles of gas inside the ball more kinetic energy and so increased the pressure. The increase in pressure made the ball get harder and so bounce higher, due to less deformation of the ball. The graph of the results from the computer show that at a lower temperature (283 K) the height decreases rapidly this is probably due to the fact that when it is so cold the pressure inside the ball decreases so making the ball softer than normal therefore it will bounce lower than normal.
Evaluation
From the conclusion I can see that the results have proven my prediction therefore they were accurate. Although in comparison to the computer programme (which would have made no faults in accuracy) the shape of the results on the graph was not the same, showing that some small error had occurred.
The results from the lower temperatures were inaccurate because it was hard to measure the ball bouncing from only a few centimetres above the ground, as the distance was so small, measuring with your eyes led to errors. It was also found that it was inaccurate to measure the height with the eyes therefore it was only roughly calculated in centimetres, not in millimetres, although this inaccuracy was overcome by the repeat readings which helped to make the results more accurate.
When looking closely at the results from temperatures: 283 K, 303 K, 353 K, and 363 K, they all fit on a straight line, this though maybe a coincidence, as the results as a whole seem to curve.
The range of results was adequate, showing a large difference between the smallest and largest temperature and enough results to make a good line of best fit. The range could have been improved by testing it every 5 degree drop.
The pattern of the results was also the same in Will’s experiment therefore it was not only true for values that I used. I would predict that it would continue beyond this range, this could be experimented by cooling the rubber in a freezer to get a lower temperature or by heating it in a liquid with a higher boiling point than water so the rubber could be tested at a higher temperature to see if it would bounce any higher than 373 K. Although there would be a limit in which the rubber could bounce, when the rubber reached it’s freezing point it would no longer bounce, but may even shatter, and if it got too hot it would simply melt or burn.
There are other aspects of the experiment which could be tested to see the effect of the height of the drop, the surface of the table, the size of the ball (different amount of gas inside the ball), if the ball was hard, for example a hockey ball. The experiment could also be tested by heating non-hollow balls to prove that it was the gas inside the squash ball that made the difference of how the ball bounced, this would be done with the same type of rubber as the one used in the squash ball and would be the same weight (24 grams).
In an extension of this experiment the pressure of the gas inside the ball could be calculated and compared with the height of bounce. The pressure could be calculated by working out by measuring the time it takes for the ball to fall and bounce back. Use this to work out the balls acceleration (∆v/t), use the acceleration to work out the force of the ball, Force = mass x acceleration (the mass being 24 grams). Now that the force is known it can be divided by the area of the gas inside the ball to give the pressure of the gas inside the ball.