Provisional Investigation
The aim of my provisional investigation is to find the best temperature to heat the squash ball to before I drop it.
Results
(1) (2) (2) -:- (1)
Conclusion
In my main investigation I will use the squash balls heated to 40°C because they are more efficient.
Method
First I will heat up the squash balls to 40°C in a water bath. I will then check the water bathe is the right temperature with a thermometer. I will use tongs to pick up the ball and take it to the surface (a table top) and lift it to a drop height o f 10-100cm in 10cm intervals. I will drop it and watch the height it bounces to using the bottom of the ball as the measuring point against the ruler. I will do five repeats for each height. I will be recording my results in a table throughout the duration of the experiment. If I have any anomalies then I will repeat the anomaly in a sixth repeat. This is to correct the error so I get a more accurate average for later on when I am processing my results. I will then measure the average of the repeats for that drop height. Next, I will draw a graph to show the average bounce height for each drop height. It will include a line of best fit.
Equipment
Squash balls
Water bath
Thermometer
Meter Ruler
Table surface
Tongs
Fair Test
To make it a fair test I will make the squash balls all the same temperature for each repeat, and make sure that the squash balls are all of the same weight (this is represented by the dot colour.
Results table
-------------------Bounce heights (cm)------------- Repeat
= Anomalous result (repeat in column 6)
Conclusion
My evidence shows me that the higher I dropped the ball from, the higher it bounced.
The trend (pattern) shown by my graph is that as the drop height is doubled, the bounce height is approximately doubled as well. For instance, when the drop height is 0.20m, the average bounce height is 4.40cm, and when the drop height is 0.40m, the average bounce height is 9.40cm.
The science that explains this trend is that when the squash ball is dropped, the energy changes from GPE to kinetic. When the ball hits the surface, energy is lost due to compression, sound and heat. As it keeps bouncing, the squash ball loses more and more energy, until it doesn’t bounce at all.
Efficiency chart
Ball weighs 0.024kg
Drop Bounce
GPE = Mass x Gravity x Height (0.024 x 10 x Drop Height)
Efficiency = GPE After -:- GPE Before (Bounce -:- Drop)
My conclusion does support my prediction because I predicted that when you have a higher drop height, the ball would bounce higher. When I did my provisional investigation, the efficiency of the squash ball heated to 40°C was 0.27 (or 27%) when dropped at 1m. When I did my experiment the efficiency of the ball dropped at 1m was 0.30 (or 30%). These results are very close to each other, even though the efficiencies of the drops in the main experiment did not completely comply with my prediction (there were a few anomalies.)
Evaluation
In the practical work, the difficult parts were keeping the squash balls at the temperature (40°C), as you had to take the balls out the water bath and do the drop very quickly to avoid them cooling down. Also, measuring the bounce height accurately was difficult, you had to make sure that you were reading the height off from the bottom of the ball, and as it was very quick you had to make sure you got it accurate.
In the results table the measurements that look strange (anomalies) are the fifth repetition for a drop height of 0.30m where the bounce height was 4cm, and the fourth repetition for a drop height of 0.70m where the bounce height was 16cm.
On the graph, the points that look strange (anomalies) are at drop heights of 0.50m, and 0.60m. These are only slight anomalies, and only because they lie off the line of best fit.
To measure things more accurately you could use a video camera to measure the bounce height, by recording the drop of the squash ball, then watching it back and pausing it on the bounce and reading off the height it reaches. This way we can make sure we get the exact bounce height, instead of just a rough estimate.
The reasons that the repeats are not all identical are we might have made mistakes when reading the bounce height. It was very hard to do as the bounce was fast and you had to be really concentrating and accurate when you were reading off the heights.
The largest range bars are for the drop heights of 0.70m (where the range is 5cm), and 1m (where the range is 4cm.)
To make this practical method more reliable, you could repeat the bounces 10 times for each drop height (instead of 5). We could also video it to check the bounce heights, make the room 40°C to keep the ball temperature constant (controlled environment).
The strange (anomalous) results might have happened because we couldn’t read the bounce height when it was too close to the surface. Or because the ball cooled down over usage, the water bath could have also cooled down. To avoid this we could stir the bath more often and leave the squash ball in the water long enough to heat up.
Extra practical work I could do to back up my conclusion would be to use the video camera method, to do more repeats, do the experiment with a different types of squash ball, to do the experiment over a different range of drop heights (1-2m), and to compare the efficiency with different types of sports balls (golf, tennis, etc).
