Further Improvements

One improvement that could be made to the experimental design would be the method of collecting data. In order to reduce human error when the motion sensor is being used, the motion sensor could be started before the balls are released, so as to ensure that the starting height of the balls would be accurately recorded.

Conclusions

Conclusions can be made that the greater the amount of borax solution used, and the higher the concentration of borax solution used, the greater the height of rebound of the ball, and thus combining the two - using a high amount and concentration of borax solution - could produce a ball that would rebound to great heights.

Limitations and Assumptions

Limitations

As mentioned in an earlier post, one limitation of this investigation is that there was human error when collecting the data. When using the motion sensor to record the movement of the balls, human reaction resulted in a difference between the time when the balls were released and the time when the motion sensor was started. This caused some of the starting heights of the balls to be inaccurate, as the motion sensor was only started after the ball was already released. This could have possible implications on the data such that the rebound ratio of the balls would not be completely accurate.

Assumptions

• Starting height of the balls remained the same for all the data collected. Due to the limitation mentioned above about human error, the measurement of the starting height of the balls was not as accurate as possible. However, since a long ruler was used to measure the starting height of the balls, the starting height can be assumed to be the same.
• Surface on which the balls bounce is the same throughout the data collection.
• All the balls are assumed to be released with the same effort, since they were allowed to freefall.
• The balls are assumed to have the same surface and shape. This is because the balls were shaped using human hands, and so will not be exactly spherical.

Data Analysis

Figure 1

Figure 2

From Figure 1, the graph shows an upward trend from 5ml of borax solution onwards. The slope is flat at the start, when 2.5ml and 5ml of borax solution was used. However, the graph starts sloping upwards from 5ml onwards, with the peak being 0.3m when 12.5ml of borax solution was used.

This can be interpreted that a greater amount of borax solution used increases the height of rebound of the ball, as the height of rebound of the ball when 12.5ml of borax was used is 87.5% higher than that of the ball made using 2.5ml and 5ml of borax. The reason why the balls made with 2.5ml and 5ml of borax solution did not bounce as high as the one made with 12.5ml of borax is probably because there was too little borax that cross-linked with the glue, thus some chains of the glue polymer may not have been properly cross-linked. The polymer would not have as much strength and so did not bounce as high as the ball which had many strong cross-linked chains. The most desirable amount of borax solution to use would thus be 12.5ml, as it produces a ball that can bounce the highest. From the upward trend of the graph, it can be predicted that using even more borax solution may even produce a ball that rebounds to an even greater height.

In Figure 2, the graph also shows an upward sloping line. However, unlike the graph in Figure 1, the line does not have a concave slope, and has a more consistent gradient throughout. This is due to the increases in the height of rebound of the ball being more consistent. The lowest point on the graph is at a height of 0.1m, when a 2% concentration of borax solution was used, and the highest point of the graph is at a height of 0.29m, when a 10% concentration of borax solution was used. This can be interpreted that a higher concentration of borax used is very effective in increasing the height of rebound of the ball, since the latter has a rebound height that is 190% of the former. The most desirable concentration of borax solution to use would be 10%, and like Figure 1, the graph also predicts that an even higher concentration of borax solution used could produce a ball that would rebound to an even greater height. Also, similar to what was explained above, the 2% concentration of borax solution may not be concentrated enough to allow the cross-linking to occur most effectively, hence the ball did not rebound as high as the ball with a 10% concentration of borax solution.

From both graphs, I can conclude that the amount of borax solution used correlates to the concentration of borax solution used, as both show an upward trend. These results prove my hypothesis as the greater the amount of borax solution used, the greater the height of rebound of the ball, and similarly, the higher the concentration of borax used, the greater the height of rebound of the ball. When making the polymer ball, combining both a high amount of borax solution and high concentration of borax solution should produce a ball that will rebound to a very great height.

Collated Data + Graphs showing relationships

Collated Data - Amount of Borax Solution:

Relationship between the amount of borax solution used and the average height of rebound of the ball:

Relationship between the amount of borax solution used and the average % rebound of the ball:

Collated Data - Concentration of Borax Solution

Relationship between the concentration of borax solution used and the average height of rebound of the ball:

Relationship between the concentration of borax solution used and the average % rebound of the ball:

I plotted graphs using both the average height of rebound of the ball and the average percentage of rebound of the ball (which used the recorded starting height of the ball), but found that the graphs using the average height of rebound of the ball were more accurate. This can be seen in the graphs above. The relationship was clearly more consistent and so this contributed to my decision to use the average height of rebound of the ball (as per 1m starting height)

Data Collection and Results

Please refer to my wikispace at this link http://21001sipdata.wikispaces.com/ to view the data collected. This is because i am unable to insert files on blogger. Thank you!

Graph showing the relationship between an 8% concentration of borax solution used to make the ball and the height of rebound of the ball

Figure 1

Graph showing the relationship between 5ml of borax solution used and the height of rebound of the ball.

Figure 2

As can be seen from these two graphs which were taken from my data, my results were sometimes inaccurate. This is mostly due to human error. Figure 1 shows the starting height of the ball to be 0.165m. This is clearly inaccurate because when collecting the data, a long ruler was used to measure the starting height of the ball, 1m. Human error most likely occurred as the time of release of the ball and the starting of the motion sensor were not at exactly the same time, due to delays in the human reaction. Thus, the motion sensor recorded the starting height of the ball after it had already been released, resulting in data whereby the starting height of the ball was inaccurate.

This limitation in human error negatively affected the results when calculating the rebound percentage of the ball based on the recorded starting height and 1st rebound height of the ball. Since the starting heights of the ball were all recorded to be different, the rebound ratios of the ball were very inaccurate and not a good measure of the actual rebound percentage of the ball.

I thus created a few more sets of the polymer balls to measure, so as to obtain more results that were more accurate. The experiment testing how the amount of borax solution used affected the height of rebound of the ball had 3 sets of balls that were tested (2.5ml, 5ml, 7.5ml, 10ml, 12.5ml x 3), while the concentration of borax solution used had 2 sets of balls that were tested (2%, 4%, 6% x 2 + 8%, 10% x 1)

Since the starting heights of the ball were all measured each time using a long ruler, I also assumed the starting heights of all the balls throughout to be of equal height, 1m. This does not make the results inconclusive because the 1st rebound height of the ball is the most important data that needs to be considered and used.

Data that was completely inaccurate was eliminated, but others that had inaccurate starting heights but accurate rebound heights were still used. I took the average of the rebound heights of the accurate graphs used, then plotting a graph showing the relationship between either the amount of borax solution used and the height of rebound of the ball or the concentration of borax solution used and the height of rebound of the ball. This enabled the data to be more consistent and accurate.

Photographs

Below are the pictures taken throughout the process of making the polymer ball. There are not many photographs as it was difficult to take pictures with my hands being dirty with all the materials especially the glue and cornstarch.

Pouring the glue into the bowl!

After adding cornstarch to the glue

Stirring the mixture with a chopstick

Pouring the mixture onto my hands to knead into a ball!

The polymer has been kneaded into a ball!

Some of the polymer balls made

Trying out: Polymer made with glue, borax and water!

Stretching the polymer

Finished balls kept in ziplock bags

When making the polymer balls, I observed that the balls made using 12.5ml of borax solution were very difficult to mould into a ball as the polymer would not stick together, while balls made using 2.5ml of borax solution were very sticky and "goopy", and were also very difficult to make as they were too much in liquid form and could not form a ball. Similarly, this was also observed when using 10% and 2% concentration of borax solution respectively.