TESTING THE BOUNCABILITY OF DIFFERENT SIZED BOUNCY BALLS
Rishi Goswami
Cary Academy
ABSTRACT
The purpose of the experiment was to see which sized bouncy ball bounces the highest:
a small one, a medium-sized one, or a large one. It was hypothesized that the small
bouncy ball would bounce the highest, since it would require the least amount kinetic
energy to bounce high, since it had the least mass. Even though the low mass would
cause it to gain less kinetic energy while falling, it was figured that this would be
overpowered by the low amount of kinetic energy that was needed to make it bounce
high. To perform the experiment, the three sizes of bouncy balls were dropped three
times each, and the average bounce height of each bouncy ball was recorded. It turned
out that the hypothesis was incorrect, as the medium-sized bouncy ball bounced the
highest of the three sizes of balls. The small bouncy ball bounced the second highest,
and the large bouncy ball bounced the lowest.
The purpose of the second experiment that was performed was to see how the
temperature of a bouncy ball affects the height it bounces. The ball that was kept at
15.6 degrees Celsius (the cold bouncy ball) bounced the highest, the ball that was kept
at room temperature (22.4 degrees Celsius) bounced the second highest, and the ball
that was kept at 40.6 degrees Celsius (the warm bouncy ball) bounced the lowest.
INTRODUCTION
The purpose of the experiment was to see what sized bouncy ball bounces the highest:
a smaller one, a medium-sized one, or a larger one.
The smaller bouncy ball had a diameter of 2.5 centimeters. It had a mass of 9.9 grams.
It was pink, with stripes on it. It felt and looked elastic, which meant that it seemed like it
would bounce well.
The medium-sized bouncy ball had a diameter of 3.3 centimeters. It has a mass of 21.2
grams. It was green, and it also had stripes. It looked and felt elastic, too.
The third, larger bouncy ball had a diameter of 4.0 centimeters. It had a mass of 42.1
grams. It was brown, and its inside was filled with a solid that seemed to make it look a
little like a meteor. This ball also seemed to be very elastic.
The first bouncy ball was made by a chemist in California named Norman Stingley. It
was made in 1965, a time when Stingley spent his extra time experimenting with rubber.
He compressed many pieces of synthetic rubber together while they were under
approximately 3500 pounds of pressure per square inch. This experimenting resulted in
a compressed rubber ball with an extreme resilience and high bounce.
The momentum of an object changes based on its mass and velocity. It is calculated
with the equation, p = m times v, where p is the momentum of the object, m is the mass
of the object in kilograms, and v is the velocity of the object in meters per second. When
one object hits another object, some or all of the momentum it had is transferred to the
object it hit. For example, when a cue ball hits a billiard ball, the momentum the cue ball
had before the collision is transferred to the billiard ball during the collision. After the
collision, the billiard ball travels with the same momentum that the cue ball previously
had. This is an example of the law of conservation of momentum, which states that
whenever objects collide, the amount of mass stays the same.
When a baseball hits a bat, the bat pushes the baseball away. In the same way, a ball
bounces off of the floor when it falls because the floor pushes the ball up. Balls fall
because they are pulled to the ground by gravity. While they are falling, they gain kinetic
energy, or energy of motion. When the balls hit the floor, the kinetic energy that was
earned deforms the ball from its original round shape to a new squashed shape. When
the ball deforms, its molecules are stretched in some areas, and tightened in the others.
As the molecules are moved around, they collide with and rub across one another.
What happens after this depends on what the ball is made out of. If it is made out of
putty, it will hit the floor and then flatten. Putty is inelastic, and therefore, it will not
bounce. Now, if the ball is made out of rubber, which is made from long-chain polymer
molecules, its lengthy molecules will be tangled together while in your hand. After the
rubber ball falls and hits the floor, its molecules will stretch for a very small amount of
time. Atomic motions within the molecules of rubber turn the molecules back into their
original, round shape. This means that a rubber ball is elastic, because it turned back
into its original shape. The rubber ball will then bounce back up using its kinetic energy
it gained earlier. The remaining energy not used to make the ball move will be turned
into warmth. Most things that bounce are sphere shaped, however things shaped like
footballs can also bounce. Objects need equilibrium, or balance, to bounce.
If each ball was to be dropped, then the ball with a diameter of 2.5 centimeters (the
smallest one) would bounce the highest, because it would require the least force to
bounce since it had the least mass. Even though it would gain less kinetic energy while
falling since it had the least mass, it was figured that this would be overpowered by it
not needing as much kinetic energy as the other two balls to bounce high.
MATERIALS AND METHOD

1 small bouncy ball with a diameter of 2.5 centimeters

1 medium-sized bouncy ball with a diameter of 3.3 centimeters

1 large bouncy ball with a diameter of 4.0 centimeters

1 meter stick
The control of the experiment was the medium-sized bouncy ball, because it was the
size that children typically play with. The independent variable was the type of bouncy
ball used for the experiment, and the dependent variable was how high each bouncy
ball bounced. The constants of the experiment were the surface the balls were bounced
on, the height they were dropped from, and the material they were made from.
First, the medium-sized bouncy ball (that had a diameter of 3.3 centimeters) was held
and then dropped from the top of a meter stick that was held up straight. The height that
the bouncy ball bounced after it hit the ground was recorded. This was done 3 times,
and then the average height that the ball bounced was found. This whole process of
dropping the bouncy ball from a meter high and seeing and recording how high it
bounced back up three times was repeated again, but the small bouncy ball (that had a
diameter of 2.5 centimeters) was used instead of the medium-sized bouncy ball. Finally,
this process was repeated one last time with the large bouncy ball (that had a diameter
of 4.0 centimeters).
A second experiment was performed to see how temperature affects the height a
bouncy ball bounces. The control of the experiment was a green bouncy ball that was
kept at room temperature. The independent variable was the temperature of the bouncy
balls, and the dependent variable was how high they bounced. The constants of the
experiment were the material used to make the bouncy balls, the size of the bouncy
balls, and the surface the bouncy balls were bounced on.
To perform the experiment, the three bouncy balls had to be at different temperatures. A
green bouncy ball was kept at room temperature. A blue bouncy ball was kept in a
bucket of ice for 15 minutes. A purple bouncy ball was kept in an incubator for 24 hours.
The green ball that was kept at room temperature ended up having a temperature of
22.4 degrees Celsius. The blue bouncy ball that was kept in ice ended up having a
temperature of 15.6 degrees Celsius. Finally, the purple bouncy ball that was put in the
incubator ended up being 40.6 degrees Celsius. First, the green bouncy ball that was
kept at room temperature was held and then dropped from the top of a meter stick 3
times onto a tiled floor. The height that it bounced back up after it hit the ground each
time was recorded, and then its average bounce height was found. This whole process
of dropping the ball from a meter high 3 times onto a tiled floor and seeing and
recording how high it bounced after hitting the ground each time was done again, this
time using the cold, blue bouncy ball. Finally, to finish the experiment, the process was
repeated one last time with the warm, purple bouncy ball.
Average Bounce Height
(cm)
RESULTS AND DISCUSSION
82
81
80
79
78
77
76
Small
Medium
Large
Size of Bouncy Ball
Figure 1: Average Bounce Height of Different Sizes of Bouncy Balls
The medium-sized bouncy ball, or the control of the experiment, bounced the highest,
with an average bounce height of 81.33 centimeters. In second place was the small
bouncy ball, which bounced an average of 79.67 centimeters high. Finally, the large
bouncy ball bounced the lowest, with an average bounce height of 78 centimeters. The
highest that the medium-sized bouncy ball bounced was 82 centimeters, and the lowest
it bounced was 80 centimeters. The highest that the small bouncy ball bounced was 80
centimeters, and the lowest it bounced was 79 centimeters. The highest that the large
bouncy ball bounced was 80 centimeters, and the lowest it bounced was 75
centimeters.
The control of the experiment (the medium-sized bouncy ball) bounced 1.66 centimeters
higher than the small bouncy ball. It bounced 6.33 centimeters higher than the large
bouncy ball. Therefore, the control of the experiment bounced higher than the other two
bouncy balls, or the variables of the experiment.
One thing that was noticed while experimenting was that the small and medium-sized
bouncy balls did not make a very loud sound when they bounced, but the big bouncy
ball did. Another thing that was noticed was that all of the balls bounced slightly to the
side in all of their trials. Finally, it was found interesting that when the balls fell and
Average Height Bounced
(cm)
bounced, they would rotate.
78.5
78
77.5
77
76.5
76
75.5
75
0
10
20
30
40
50
Temperature (degrees Celsius)
Figure 2: Bounce Height of Different Temperatures of Bouncy Balls
In the second experiment, there was an inverse relationship between the temperature of
a bouncy ball and its bounce height. The bouncy ball that was kept at a temperature of
15.6 degrees Celsius bounced the highest, having an average bounce height of 78.33
centimeters. In second place was the ball that was kept at room temperature (22.4
degrees Celsius), which had an average bounce height of 76.33 centimeters. Finally, in
last place was the ball that was kept at 40.6 degrees Celsius, which had an average
bounce height of 75.33 centimeters. The highest that the green bouncy ball kept at
room temperature bounced was 79 centimeters, and the lowest that it bounced was 74
centimeters. The highest that the blue bouncy ball kept at 15.6 degrees Celsius
bounced was 79 centimeters, and the lowest that it bounced was 78 centimeters.
Finally, the highest that the purple bouncy ball kept at 40.6 degrees Celsius bounced
was 76 centimeters, and the lowest that it bounced was 75 centimeters.
It was noticed while experimenting that the bouncy ball kept at a temperature of 15.6
degrees Celsius seemed to fall down faster than the other two bouncy balls. Also, the
warm bouncy ball felt slightly softer than the bouncy ball kept at room temperature did,
and the cold bouncy ball felt slightly harder than the bouncy ball kept at room
temperature.
CONCLUSIONS
The hypothesis was found to be incorrect, as the medium-sized bouncy ball bounced
higher than the smaller bouncy ball. The medium-sized bouncy ball must have bounced
the highest because it gained a good amount of kinetic energy while falling, and it also
did not need too much kinetic energy to bounce high. On the other hand, the large and
small bouncy balls, although they either gained more kinetic energy or didn’t need as
much kinetic energy to bounce high compared to the medium-sized bouncy ball (since
they had either a higher or a lower mass), the large bouncy ball also needed more
kinetic energy to bounce high, and the small bouncy ball did not gain a lot of kinetic
energy while falling. These things offset the large and small bouncy balls’ advantages
over the medium-sized bouncy ball.
This experiment could be improved by using more bouncy balls of different sizes in
between the ones used, to see if there are any sizes of bouncy balls that bounce even
better than the medium-sized one that was used in this experiment. Another
improvement could be to have someone hold the meter stick straight to make sure that
it isn’t tilted, therefore making the results more accurate. Finally, a third experimental
improvement could be to use balls that were all made by the same company to make
the results more accurate. A future experiment could be to see which surface bouncy
balls bounce best on.
In the second experiment, there was nothing “mind-blowing” that was found. The only
things that were noticed while experimenting that were not shown in the data were the
things that were stated in the Results and Discussion section.
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1/27/14.
Wikipedia. "Bouncy ball." Wikipedia.org. Wikipedia, 21 Dec. 2013. Web. Accessed
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