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Hockey Puck Conservation of Momentum Blog


Conservation Of Momentum With Hockey Pucks


Link to Video: https://youtu.be/LkCw82xbROg


In this blog, the conservation of momentum can be shown using one hockey puck of 0.05 kg that has a velocity of 0 m/s while another hockey puck of 0.15 kg that has a velocity of 2.791 m/s. That number is found by plugging the video into Logger Pro and calculating the velocity just before the collision. After plugging the information into Logger Pro, the initial velocity of m1 is found to be 2.791 m/s.

Velocity Graph of V1 (Initial)



The heavier hockey puck is pushed (by my sister) in the positive x direction towards the stationary lighter puck. The final velocity of the two pucks can be calculated using the conservation of momentum equations.

m1 = 0.15 kg                            V1 (initial) = 2.791 m/s
m2 = 0.05 kg                            V2 (initial) = 0 m/s

(m1 * v1 (initial)) + (m2 * v2 (initial)) = (m1 * v1 (final)) + (m2 * v2 (final))
V1 (initial) + V1 (final) = V2 (initial) + V2 (final) --> V1F = V2F +V2I - V1I
(0.15*2.791) + (0.05*0) = (0.15*V1F) + (0.05*V2F)
V1F = V2F + 0 - 2.791

0.4186 = (0.15*(V2F + 0 - 2.791)) + (0.05*V2F) 
 0.4186 = 0.15*V2F - 0.4186 + 0.05*V2F
0.8373 = 0.20*V2F --> V2F = 0.8373/0.2 
V2F = 4.187 m/s

(0.15*2.791) + (0.05*0) = (0.15*V1F) + (0.05*4.187)
0.4186 = 0.15*V1F + 0.209 --> V1F = 0.209/0.15
V1F = 1.395 m/s

After the two pucks collide, the heavier puck is still traveling in the positive x direction with a velocity of 1.395 m/s while the lighter puck is traveling in the positive x direction as well but with a velocity of 4.187 m/s. These numbers were then checked using Logger Pro. In Logger Pro, the V1F was calculated to be 1.69 m/s immediately following the collision. The V2F was calculated to be 4.025 m/s immediately following the collision. After the collision, due to friction and air resistance and even the wind, the two pucks quickly decelerated and came to a stop. Both final velocities found in Logger Pro are very close to the numbers found by solving the equations. There is room for error from the fact that the 2.791 m/s of the V1 initial may have been slightly off which would have affected the rest of the answers. Also there could have been error when plotting the points in Logger Pro which would have made the numbers slightly different. Finally, the numbers may have been different than the ones calculated because masses calculated may have been a few decimal places off therefore making the two velocities different values.

Velocity Graph of the V1F 


Velocity Graph of the V2F





Technically, after the two pucks collide, they do not continue to travel only the x direction, but I was unable to calculate the angle that the two pucks travelled after the collision, although the angle would have been very small. Also, I tried to slide the pucks on an area that was icy so the friction factor is low but there is still friction present as well as air resistance although the air resistance would be low as well. So overall, these numbers are not exact by any means, but if air resistance, friction, and the angles are excluded, then this can be seen as a great example of conservation of momentum.

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