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Snow Day Blog! Medicine Ball and Volleyball Collision

Isabella Jacavone - Period E

For my Snow Day blog, I decided to test the conservation of momentum between a medicine ball that's used for working out and a basic volleyball. The medicine ball was labeled with a big white "4 kg" so I, as an observing experimenter am inclined to believe that the mass of the medicine ball is 4 kg, meanwhile I had to do some digging to find out the mass of the volleyball. I did this by looking up the approximate mass of an indoor volleyball with the dimensions and pressure of my volleyball. The mass that I found was 9.9 ounces, and using Google's help I converted the mass of the volleyball to .281 kg. 

In my experiment, I had the volleyball rest on my patio 1 meter in front of the medicine ball. While the volleyball was at rest, I gave the medicine ball a healthy push and let physics do its thing. 


Taking this video and plugging it into Logger Pro, I began plotting points from the center of the medicine ball until the end of the clip. I did the same for the volleyball. The resulting X displacement vs. time graph for both the medicine ball and the volleyball looks as such:

Finding the line of best fit for each graph, I was able to find the velocity of the medicine ball before the collision, 0.94 m/s 

Medicine Ball before the Collision:
V: 0.94 m/s
M: 4kg
p = mv
p= (4)(0.94) 
momentum = 3.76 kg m/s

Volleyball before the Collision:
V: 0 m/s
M: .281 kg 
p=mv
p=(0.281)(0)
momentum = 0 kg m/s 

Medicine Ball/Volleyball System after collision
V; 0.73 m/s
M: (m1+m2) = 4.281 kg
p=mv
p=(4.281)(0.73)
momentum= 3.125 kg m/s

As we learned in class, momentum is conserved in any collision, but energy is not. 

KEi (KE of Medicine ball) = (.5)mv^2 = (.5)(4)(0.94)^2 = 1.767 J
The volleyball had no KE because it was not moving before the collision 

KEf (KE of the system after the collision) = (.5)(m1+m2)vf^2 = (.5)(4.281)(0.73)^2 = 1.141 J

change in KE = KEi - KEf = 1.767 J - 1.141 J = 0.626 J lost in the collision, which is a 35% decrease in KE. 

In conclusion, I can evaluate that this collision was in fact an inelastic collision; energy  (specifically 35%) is lost in the collision yet momentum remains conserved. The lost energy can be transferred into sound, bounce, and any other movements of the systems. I am sure that more could be done to limit the outside factors affecting the experiment, but this simple backyard experiement does an awful good job representing the conservation of momentum in a collision and the loss of energy that results. Viva las physics!





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