Moment of inertia of a charged spinning top

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Discussion Overview

The discussion centers around the calculation of the moment of inertia of a charged spinning top submerged in an electromagnetic field. Participants explore the relationship between charge, electromagnetic fields, and moment of inertia, considering both theoretical and conceptual implications.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant seeks to calculate the moment of inertia for a charged spinning top in an electromagnetic field, having previously calculated it for an uncharged top.
  • Another participant expresses skepticism about the relevance of charge to moment of inertia, suggesting that moment of inertia is based solely on mass distribution.
  • Some participants propose that the electric field could generate a dipolar moment, potentially affecting the rotation of the spinning top.
  • There is a claim that while forces and torques may change due to the electromagnetic field, the moment of inertia itself remains constant.
  • A participant questions whether the dipolar moment could be considered an analogue to moment of inertia in an electromagnetic context.
  • Discussion includes an analogy involving a charged ballerina executing fouettes in an electromagnetic field to illustrate the concepts being debated.
  • One participant clarifies that moment of inertia is defined as the resistance to rotational acceleration and is determined by mass and dimensions, independent of motion.
  • There is a suggestion that the original poster may be confusing momentum with moment of inertia.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between charge, electromagnetic fields, and moment of inertia. There is no consensus on how these factors interact, and the discussion remains unresolved.

Contextual Notes

Participants highlight the distinction between moment of inertia and the effects of forces or torques, indicating that the moment of inertia is not influenced by external fields, though the motion of the object may be affected.

JCOM44
How can I calculate the moment of inertia of a spinning top with charge Q submerged in an electromagnetic field?

I've already calculated it for the case with no charge, but I don't know how to do this.
 
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I'm not aware of any context where charge has anything to do with the moment of inertia.
 
But the electric field generates a dipolar moment, which makes the spinning top rotate different affecting the moment of inertia, isn't that right?
 
That sounds to me like an object with a particular moment of inertia, based only on the location of it's mass, reacting to a force from the electric field. The moment of inertia is not a function of the force field.
 
JCOM44 said:
isn't that right

No.

The moment of inertia is the same. The forces and torques on the top could be different, but the moment of inertia is the same.
 
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Can't I consider the dipolar moment as an electromagnetic analogue of the moment of inertia?
 
I don't know what good that will do.
 
Then would you say that when we have a charged spinning top with a defined moment of inertia and it is suddenly exposed to an electromagnetic field, the way it rotates won't change?
 
If the field applies a force or torque to the top, it's motion will change. But it's moment of inertia will not.
 
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  • #10
Maybe it will help if I put it this way: would anything change if you put a (charged) ballerina in an electromagnetic field to execute her fouettes?



Ballerina's would make excellent physicists.
 
  • #11
An object's moment of inertia is merely the extent to which it resists rotational acceleration about a particular axis. It's a product of the object's mass and dimensions, it actually has nothing to do with motion.

Take the moment of inertia of a solid sphere for example, which can be expressed as
$$I=\frac{2}{5}mr^2$$
As you can see, motion doesn't play a part whatsoever (we're talking classically here).
 
  • #12
Even a force like friction doesn't change the moment of inertia.

Perhaps the OP is confusing momentum and moment of inertia?
 

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