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Motion Analysis - What I am doing Wrong?

Question asked by Mauricio Martinez-Saez on Aug 9, 2009
Latest reply on Sep 3, 2009 by Ian Hogg

I take some time to model a toy that most of you have seen: the old Swinging Balls Apparatus, and them run a Motion study to see if I can get the actual results... however, when I place one ball on an elevated position and let it swing under gravity and hit the other six ball, after the impact all the balls show a swing motion, which is not the real effect you get with the actual apparatus.


the swinging balls apparatus must satisfy all the energy conservation laws, not just one or two. The only way to satisfy both momentum and energy conservation in this case is for one ball to go in and one ball to go out, or two balls in, two balls out, but I am not able to get the proper results.


What is happening?  Do I have something wrong on the model?  or is that Motion can not perform the correct calculations and simulate the behavior of the actual apparatus?


Maybe I am not using the proper parameters for contact, particularly to define the impact parameters (damping, penetration, etc.) or is that the software perform an incorrect calculation?


It look to me like the software is just taking care of the conservation of energy not the momentum where the effect to the mass and velocity of the ball being lifted and released under gravity force to collide with the other ball result in:


1m v1 = 7m v1/7


Since after impact all the balls swing at a lower momentum.  This may satisfy the energy conservation law but is not correct, since both energy and momentum should be conserved.


I believe that the problem is that I am not using the proper parameters when I define the contact, particularly to define the friction and impact parameters (damping, penetration, etc.), or maybe I am using the wrong "integrator"


Maybe someone out there (a GURU on Motion Simulation), can take a look at the model and make it work... entering the correct parameters, I will like to see those, once the model is working properly.


Attached is a zip file containing the assembly and the Motion Study (Motion Analysis Add-In need to be active). The assembly is SW 2009 sp 4.0