Question about two torques on rigid body.

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Discussion Overview

The discussion revolves around the dynamics of a massless, rigid rod with motors attached to each end, which are connected to massive discs. Participants explore the effects of torque generated by the motors on the rod and the discs, particularly focusing on scenarios where the discs are spun in the same or opposite directions. The inquiry includes considerations of net torque and force in the absence of external influences like gravity or friction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether there is a net torque or force acting on the system, given the conditions specified.
  • Another participant asserts that the rod will rotate along with the discs about their common axis when both discs are spun in the same direction.
  • A participant expresses uncertainty regarding the existence of a common axis when the discs are spun in opposite directions, suggesting that this scenario may lead to torsion.

Areas of Agreement / Disagreement

Participants generally agree that the rod will rotate with the discs when spun in the same direction. However, there is disagreement and uncertainty regarding the behavior of the system when the discs are spun in opposite directions, particularly concerning the concept of a common axis and the implications of torsion.

Contextual Notes

The discussion does not resolve the implications of torsion or the conditions under which a common axis exists when the discs are spun in opposite directions. Assumptions regarding the absence of external forces and the nature of the torque interactions are also not fully explored.

Crappinni
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Hi, here's the question:

A massless, rigid rod has motors attached on each end. The motors are each connected to a massive disc, and the motors accelerate the discs in the directions indicated by the arrows.

Due to the torque from the each motor on its disc and hence that on the rod and other disc, is there a net torque or force?

Assuming there are no other forces (like gravity or friction), what will happen?

Additionally, if both discs are spun in the same direction, what happens?

Thanks!
 

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What do you expect to happen?
Clearly, the rod will rotate along with the discs about their common axis.
 
R Power said:
What do you expect to happen?
Clearly, the rod will rotate along with the discs about their common axis.

Thanks for answering.

I'm sure that's the case when both discs are spun the same way because of the torque couple. But when they are spun in opposite directions, why would they have a common axis?
 
I'm sure that's the case when both discs are spun the same way because of the torque couple. But when they are spun in opposite directions, why would they have a common axis?
in case discs are spun in opposite directions there will be the case of torsion.
 

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