Moment applied on a circular disc

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Discussion Overview

The discussion revolves around the effects of applying a moment to a circular disc, specifically comparing the scenarios when the moment is applied at the center versus when it is applied at a point not at the center. Participants explore the implications of these applications on the rotation of the disc and the calculation of angular frequency.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant states that applying a moment at the center of the disc will result in angular acceleration, indicating that the disc will rotate.
  • Another participant suggests that applying a moment not at the center will still cause the disc to rotate about the center, emphasizing that the moment acts as a free vector.
  • A later reply questions the clarity of the explanation and requests further elaboration on the topic.
  • Another participant explains that applying a tangential force at any point on the disc will initiate rotation about a fixed axis, but notes that if there were no fixed axis, the disc would rotate around its center of mass instead.

Areas of Agreement / Disagreement

Participants express differing views on the implications of applying moments at different points on the disc, with some agreeing on the concept of fixed axes while others seek clarification on the mechanics involved. The discussion remains unresolved regarding the specifics of angular frequency calculation and the effects of the applied moment.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about fixed axes and the conditions under which the disc rotates. The dependence on definitions of moments and forces is also noted but not resolved.

chandran
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moment on a circular disc(moment applied in the centre)
A circular disc is hinged in the centre. I am applying a moment at the centre. The result is that the disc will rotate with an angular acceleration "a"

moment on a circular disc(moment applied not in the centre)
A circular disc is hinged in the centre. I am applying a moment at some point in the disc but not at the centre. How can i calculate the angular frequency. What is the theory? Will the disc rotate?
 
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For your moment not applied at the center, it will still rotate about the center. The moment is a free vector, it can act anywhere you put it. It will cuase rotation around the fixed point of the body, if that point allows for rotation in the direction of the moment.

EDIT: What I said applies for a couple moment, if that's what you mean.
 
Last edited:
i am not getting. pls elaborate.
 
Because one is incorporating a fixed rotation axis for the disk, it does not matter where on the disk other than its axix that you apply a tangental force to initiate rotation about that axis.
This would NOT occur if there were no fixed axis. In that case, the disk would rotate around its center of mass, which can be substantially different that the location of a fixed axis.
With a "fixed axis", centered or not, you are "forcing" rotation to occur around that axis.
 

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