Interesting Inelastic Collision

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SUMMARY

The discussion centers on an inelastic collision involving a translating and rotating rigid disk that tips a rod at rest, resulting in a combined rigid body. Key calculations demonstrate that kinetic energy (KE) is not conserved during this collision, despite the contact point having zero relative velocity. The loss of KE is attributed to work done by friction at the contact patch, which facilitates the conservation of angular and linear momentum, while no pivot force or torque is exerted through the rod.

PREREQUISITES
  • Understanding of inelastic collisions
  • Knowledge of angular and linear momentum conservation
  • Familiarity with rigid body dynamics
  • Basic principles of friction and its effects on motion
NEXT STEPS
  • Study the principles of inelastic collisions in detail
  • Explore the conservation of angular momentum in rigid body systems
  • Investigate the role of friction in collisions and its impact on energy loss
  • Review examples of rigid body dynamics involving multiple objects
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Physics students, mechanical engineers, and anyone interested in understanding the dynamics of collisions and energy conservation in rigid body systems.

stanli121
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Homework Statement


Consider a translating and rotating rigid disk. As it movies, it just tips the top of a rod that is initially at rest. The puck sticks to the rod, forming a rigid body that looks like a
popsicle that after the collision moves on as one rigid body. I did the calculations to show that KE is not conserved but I'm now wondering how KE is not conserved if the contact point of the disk has zero relative velocity with respect to the rod?

Homework Equations





The Attempt at a Solution


Thus far, I am thinking that there is some work done by friction at the mutual contact patch that allows the new rigid body to rotate in such as way as to conserve angular and linear momentum. There is no pivot through the rod so that does not exert a force/torque. Something like 'the rod bends' or 'the disk deforms' seems less than satisfactory. Any ideas as to explain the loss in KE would be much appreciated.
 
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hi stanli121! :smile:

the rotation is irelevant …

the kinetic energy is lost for the same reasons as when a non-rotating object hits the back of something and sticks to it :wink:
 

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