What is the angular velocity in the center of a rotating disc?

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Discussion Overview

The discussion centers on the concept of angular velocity in the context of a rotating disc, specifically examining the angular velocity at the center of the disc and its implications for linear (or tangential) velocity. The scope includes theoretical considerations and potential implications of different physical scenarios.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that the angular velocity at the center of a rigid body disc is the same as at any other point on the disc.
  • Another participant questions the terminology used, asking if "linear velocity" refers to tangential velocity and inquires about the implications when the position vector is very small.
  • A follow-up response clarifies that if angular velocity is constant, tangential and linear velocities are equivalent, but emphasizes that a very small position vector results in a very small linear velocity.
  • Another participant asks about non-classical cases, suggesting a potential exploration of scenarios beyond classical mechanics.

Areas of Agreement / Disagreement

Participants express differing views on the terminology and implications of linear versus tangential velocity, and the discussion remains unresolved regarding the implications of very small position vectors and non-classical cases.

Contextual Notes

The discussion does not resolve the definitions of linear and tangential velocity in the context of very small position vectors, nor does it clarify the implications of non-classical scenarios.

Seth Greenberg
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I have a disc. The center of the disc is its center of mass and the motion of the disc is purely rotational (no translation). What is the angular velocity in the center of the rotating disc?
 
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Is this a statement or is there a question in there somewhere?
 
What is the angular velocity in the center of the rotating disc?
 
Assuming that the disk is a rigid body, its angular velocity is ##\vec \omega## at its center and at any other point on it. It is the linear velocity ##\vec v=\vec \omega \times \vec r## that depends on the position vector ##\vec r## and is zero on the axis of rotation. Different points on the disk have different linear velocities but the same angular velocity about the axis of rotation.
 
By 'linear velocity' you mean tangential velocity? What happens if ##\vec{r}## is not zero but very, very small, say the plank length ##\ell_P## and ##\vec{\omega} = 1##?
 
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Seth Greenberg said:
By 'linear velocity' you mean tangential velocity? What happens if ##\vec{r}## is not zero but very, very small, say the plank length?
If ##\vec \omega## is constant, as I assume to be the case here, "tangential" and "linear" velocity are the same. When ##\vec{r}## is not zero but very, very small, then the linear velocity classically is not zero but very, very small.
 
What is the non-classical case?
 
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