This discovery also confirms my hypothesis that air pressure in a
volleyball affects its rebound height.
In “The Physics of Rebound Height” section of my paper, I
said the rebound height of a deflated volleyball should be less than the rebound height when it is
inflated.
The graph visibly proves my prediction was correct because as psi increased, the
rebound height of the ball always increased as well.
This trend is due to energy loss from air
resistance and the sound and heat given off during the ball’s collisions with the ground.
Also, the
higher collision times with a deflated volleyball than an inflated one causes a lower rebound
height for balls with lower internal air pressures.
As previously stated, in my trials the volleyball
did not return to its original height when it was bounced because it lost energy when it hit the
ground.
The collision time for the volleyball-gym floor collision affected the rebound height as
well because it had an inverse relationship with the force acting on the volleyball during the
collision since impulse is constant for constant masses.
Logically, a volleyball with less air
pressure has less air molecules.
This difference in molecule quantity causes a deflated volleyball
to deform more when it hits the ground and take longer to return to its original shape after
impact.
Conclusion
In this laboratory investigation, I measured and graphed the rebound heights of a
volleyball dropped from 50.00 inches in the air at various pressures.
This experiment confirmed
the direct relationship between the pressure of a volleyball and the rebound height.
I calculated
the relationship to be 2.9 cm/psi ± 0.8 cm/psi.
Although I could not find any data on the
relationship between cm of rebound height and internal air pressure in psi, the results of this
investigation conform to those of other investigations about the rebound height of balls on gym
floors because the results show that rebound height increases as the pressure increases. My graph
shows me that if I want a volleyball to bounce up to my waist (which is about 38.00 inches above
the ground), when dropped from my eye level (which is about 50.00 inches in the air), I would
have to apply a force to the ball in order to increase the rebound height of the ball.
This is true
because the maximum rebound height of the ball at any pressure is about 83.75 cm or 32.97
inches at 9 psi.
This investigation also confirmed that rebound height of a volleyball has less magnitude
than initial height.
I can conclude that this phenomenon is caused by the energy loss from air
resistance and the sound and heat that are given off during the collision with the ground.
Therefore, elastic potential energy of a deflated ball must be less than the elastic potential energy

of an inflated ball.
Due to this fact, the spring constant of an inflated ball must be significantly
larger than that of a deflated ball.
Elastic potential energy is equal to the product of the spring
constant of a spring or a ball and the distance the ball is deformed squared.