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.

Experimental Design - Concentration of Borax Solution

Experiment testing the concentration of the borax solution:

Independent variable: The concentration of the borax solution used.

Dependent variable: The height of the 1^st rebound of the ball.

Controlled variables:

• Amount of borax solution used
• Type of glue used
• Amount of glue used
• Type of cornstarch used
• Amount of cornstarch used
• Time given for the mixture to react on its own
• Height from which the ball is dropped
• Effort with which the ball is released (free fall)

Apparatus and materials

• 30g of Sodium Borate (Borax Powder) (in total)
• 180ml of PVA (Polyvinyl Acetate) White Glue (in total)
• 500ml of Warm Water (in total)
• 180g of Cornstarch (in total)
• Electronic Balance
• 2 Measuring Cylinders
• 2 Plastic Bowls
• 1 Pair of Chopsticks
• Stopwatch
• Long ruler (1m)
• Motion Sensor
• Data Logger

Methodology

Step 1 – Using the electronic balance, measure 2g of sodium borate.

Step 2 – Measure 100ml of warm water using the measuring cylinder. Pour the water into one of the plastic bowls.

Step 3 – Pour the sodium borate into the bowl containing the water. Stir the mixture using one of the chopsticks until the sodium borate has dissolved completely.

Step 4 – Using the other measuring cylinder, measure 15ml of PVA glue. Pour it into the other small bowl.

Step 5 – Measure 15g of cornstarch using the electronic balance and pour it into the bowl containing the PVA glue.

Step 6 – Using the measuring cylinder that was used to measure the water, measure 7.5ml of the borax solution that was made. Pour it into the bowl containing the cornstarch and PVA glue.

Step 7 – Leave the mixture for 15 seconds, timing this with the stopwatch.

Step 8 – Using the remaining chopstick, stir the mixture evenly until it thickens enough to be able to knead into a ball.

Step 9 – Remove the mixture from the bowl and knead and roll it with your hands to form a ball. Leave the ball to dry.

Step 10 – Measure a height of 1m using the long ruler. Position the ball at this height, with the bottom of the ball at the 1m mark. Place the motion sensor 0.2m above the ball.

Step 11 – Release the ball from a height of 1m, recording the movement of the ball with the motion sensor.

Step 12 – Repeat steps 10 and 11 two more times.

Step 13 – Repeat steps 1-12 using 4g, 6g, 8g, and 10g of sodium borate.

Experimental Design - Amount of Borax Solution

Experiment testing the amount of borax solution used:

Independent variable: The amount of borax solution used.

Dependent variable: The height of the 1^st rebound of the ball.

Controlled variables:

• Concentration of the borax solution
• Type of glue used
• Amount of glue used
• Type of cornstarch used
• Amount of cornstarch used
• Time given for the mixture to react on its own
• Height from which the ball is dropped
• Effort with which the ball is released (free fall)

Apparatus and Materials

• 4g of Sodium Borate (Borax Powder)
• 180ml of PVA (Polyvinyl Acetate) White Glue (in total)
• 100ml of Warm Water
• 180g of Cornstarch (in total)
• Electronic Balance
• 2 Measuring Cylinders
• 2 Plastic Bowls
• 1 Pair of Chopsticks
• Stopwatch
• Long ruler (1m)
• Motion Sensor
• Data Logger

Methodology

Step 1 – Using the electronic balance, measure 4g of sodium borate.

Step 2 – Measure 100ml of warm water using the measuring cylinder. Pour the water into one of the plastic bowls.

Step 3 – Pour the sodium borate into the bowl containing the water. Stir the mixture using one of the chopsticks until the sodium borate has dissolved completely.

Step 4 – Using the other measuring cylinder, measure 15ml of PVA glue. Pour it into the other small bowl.

Step 5 – Measure 15g of cornstarch using the electronic balance and pour it into the bowl containing the PVA glue.

Step 6 – Using the measuring cylinder that was used to measure the water, measure 2.5ml of the borax solution that was made. Pour it into the bowl containing the cornstarch and PVA glue.

Step 7 – Leave the mixture for 15 seconds, timing this with the stopwatch.

Step 8 – Using the remaining chopstick, stir the mixture evenly until it thickens enough to be able to knead into a ball.

Step 9 – Remove the mixture from the bowl and knead and roll it with your hands to form a ball. Leave the ball to dry.

Step 10 – Measure a height of 1m using the long ruler. Position the ball at this height, with the bottom of the ball at the 1m mark. Place the motion sensor 0.2m above the ball.

Step 11 – Release the ball from a height of 1m, recording the movement of the ball with the motion sensor.

Step 12 – Repeat steps 10 and 11 two more times.

Step 13 – Repeat steps 1-12 using 5ml, 7.5ml, 10ml and 12.5ml of borax solution.

Other Ideas

After conducting background research on this topic, I considered also testing how the amount of glue and cornstarch used affects the height of rebound of the ball. This is because they are both important components in making the polymer ball.

I also found out that adding more cornstarch would indeed have an effect on the height of rebound of the ball. More cornstarch would increase the elasticity of the ball by allowing binding the molecules of the polymer more tightly, thus allowing the ball to retain its shape better when it is deformed (e.g. being thrown on the ground). An increased elasticity would increase the energy of the ball when it is released, thus possibly causing an increase in the height of rebound of the ball.

Glue on the other hand, is a flexible polymer that gives the ball its strength, and is also the component that cross-links to itself when reacted with sodium borate. Thus, a greater amount of glue might increase the strength of the ball and may allow it to rebound to a greater height.

However, after more consideration, I realized that the investigation would not be a fair one if I were to test these two variables. This is because when the amount of glue or cornstarch is varied, the difference in the amounts added would be enough to cause the balls to be of different sizes. More than one variable would then be tested at the same time, the amount of glue or cornstarch used, and the size of the ball, making the experiment an unfair one. The results would also be inconclusive as I would be unable to deduce which factor was the one contributing to any differences in the height of rebound of the ball.

Research on the procedure for making the ball

After researching on the different methods to form the polymer ball, I found out that there are mainly 3 different types of methods used to create the ball. The first method involves borax, glue and water, the second using only borax and glue, and the last using borax, glue and cornstarch. I tried out all three methods as my research showed that all 3 methods produce varying results.

The ball made using borax, glue and water was very watery and slimy, and was more of a non-newtonian fluid. It was unable to form a ball and bounce.

The second ball made using only borax and glue was very sticky and was unable to thicken enough to be able to hold its shape properly, thus a ball could not be formed.

The third ball made using borax, glue and cornstarch could be shaped into a ball and could bounce. Research has also shown that cornstarch helps to bind the molecules of the polymer together, allowing it to hold its shape better and giving the ball the property of elasticity.

I thus decided to use the third method for making the polymer ball, narrowing my search on how to make the ball to just this method.

Below is one example of the process of making the polymer ball, taken from the website < http://mistralni.co.uk/articles/?p=254>

What You Will Need:

• Borax

• Cornstarch

• PVA glue

• Warm Water

• Food Colouring

• Measuring Spoons

• Spoon or craft stick to stir the mixture

• 2 small plastic cups or other containers for mixing

• Marking Pen

• zip-lock plastic bag

Instructions

1. Label one cup ‘Borax Solution’ and the other cup ‘Ball Mixture’.

2. Pour 2 tablespoons warm water and 1/2 teaspoon borax powder into the cup labelled ‘Borax Solution’. Stir the mixture to dissolve the borax. Add food colouring.

3. Pour 1 tablespoon of glue into the cup labelled ‘Ball Mixture’. Add 1/2 teaspoon of the borax solution you just made and 1 tablespoon of cornstarch.

4. Allow the ingredients to interact on their own for 10-15 seconds and then stir them together to fully mix. Once the mixture becomes impossible to stir, take it out of the cup and start moulding the ball with your hands.

5. The ball will start out sticky and messy, but will solidify as you knead it.

6. Once the ball is less sticky, go ahead and bounce it.

7. You can store your plastic ball in a sealed zip lock bag when you are finished playing with it.

However, most of the procedures that I found online had measurements that are not very accurate and specific, as can be seen above where teaspoons and tablespoons are used for the different amounts of each material. Thus, based on the online references, I made changes to the procedure as well as the apparatus and materials so that the process would be more accurate.

As the different references described different amounts of borax solution to use, such as 2.5ml of borax solution, 5ml of borax solution, 7.5ml of borax solution, or 10ml of borax solution, I decided to test all these different amounts in my experiment, as well as 12.5ml of borax solution.

I also converted all the teaspoons and tablespoons into proper specific measurements.

1 teaspoon = 5ml

1 tablespoon = 30ml

Below are some of the references I used for the procedure:

• Chemical News

http://mistralni.co.uk/articles/?p=254

• Blogpost, Amy Huntley

http://www.theidearoom.net/2009/07/make-bouncy-ball.html

• National Chemistry Week, 0ctober 16-22 2005, American Chemical Society; Meg A Mole’s Bouncing Ball

https://portal.acs.org:443/preview/fileFetch/C/WPCP_008377/pdf/WPCP_008377.pdf

• Drexel University, National Science Foundation, School District of Philadelphia; Drexel-SDP GK-12 Activity; Bouncing glue balls

http://gk12.coe.drexel.edu/modules/doc/Valerie_Binetti/Bouncing%20Glue%20Balls.pdf

Appendix D - Proposal

Topic of investigation:

Bouncing polymer ball

A – Observations Made

When my sister was bouncing a polymer ball (silly putty), I was curious as to what the ball was made of. I found out that it was made of borax (sodium tetraborate), PVA glue (polyvinyl acetate) and cornstarch. Learning that the reaction between borax and the polymer in glue, PVA, allows the ball to be able to bounce, I decided to test how borax affects the elasticity of the ball.

B – Research Question

Does the amount of borax used affect the height of rebound of the ball?

Does the concentration of borax used affect the height of rebound of the ball?

C – Hypothesis Statement

The greater the amount of borax, the greater the height of rebound of the ball.

The higher the concentration of borax, the greater the height of rebound of the ball.

D – Short summary of research done of the area of investigation

A molecule is two or more atoms bonded together by an exchange or sharing of electrons. Molecules made of long chains of atoms or groups of atoms are called polymers.

Some background research on this topic are that the polymer ball is made from the reaction between glue, which contains the polymer called polyvinyl acetate (PVA), and borax (sodium borate). The covalent bonds along the chain of PVA are strong, but the bonds between chains are weak. By adding borax to PVA, it allows the formation of strong cross-links between chains, forming a stronger and more elastic polymer.

The weak intermolecular bonds that hold the polymer together provide flexibility and rotation about the chain of the cross-linked polymer. Cornstarch helps to bind the molecules together, giving the ball the property of elasticity as it helps to maintain the shape of the ball. This flexibility and elasticity makes the polymer an elastomer, which has elastic properties and will recover its original size and shape after being deformed. Thus, when the polymer hits the ground, it will be able to bounce back up. It is said that cross-linking may increase the strength of the polymer, and since a greater amount and concentration of borax solution used would increase the number of cross-links, it would increase the strength of the polymer, allowing it to bounce higher.

E- Bibliography

• Carnegie Mellon; 2009 Colloids, Polymers and Surfaces Program Outreach Project Internet: <http://gelfand.web.cmu.edu/scimodules/3._Glue_Putty.html>
• <http://matse1.matse.illinois.edu/polymers/f.html>
• <http://www.hometrainingtools.com/fun-indoor-chemistry-projects/a/1464/>
• <http://www.sciencebob.com/blog/?p=558>
• Lecture Connections; Polymers: Slime http://icn2.umeche.maine.edu/genchemlabs/slime/lecpolymers2.htm
• Web Site/Word Document

9a-Polymer Cross-Linking

http://www.cdlilly.com

• Anne Marie Helmenstine, Ph.D., About.com Guide

http://chemistry.about.com/od/demonstrationsexperiments/ss/bounceball.htm

• National Chemistry Week; October 16-22, 2005, American Chemistry Society

https://portal.acs.org:443/preview/fileFetch/C/WPCP_008377/pdf/WPCP_008377.pdf

• http://siriusscience.pbworks.com/w/page/20797045/How-does-borax-affect-the-stretchiness-of-polymers