Moment of Inertia for 2D Rectangle: Does it Depend on Both Sides?

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Homework Help Overview

The discussion revolves around the moment of inertia of a two-dimensional rectangle with sides a and b, specifically questioning whether it depends on both dimensions when the axis of rotation is parallel to one of the sides and passes through the center of mass.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the formula for moment of inertia and consider the implications of the axis of rotation being parallel to one side. Questions arise regarding the dependence on both dimensions and the interpretation of the moment of inertia in terms of parallel strips.

Discussion Status

The discussion is ongoing, with participants examining different perspectives on the moment of inertia. Some guidance has been offered regarding the interpretation of the formula and the role of mass distribution, but no consensus has been reached.

Contextual Notes

Participants are considering the implications of the axis of rotation and how it affects the moment of inertia, with some expressing confusion about the dependence on both dimensions. There is an emphasis on understanding the physical setup and assumptions involved in the problem.

peripatein
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Hi,

Homework Statement


Will the moment of inertia of a two dimensional rectangle (with sides a, b) whose axis is parallel to one of its sides and passes through its center of mass, be (1/12)M(a2+b2)?


Homework Equations





The Attempt at a Solution

 
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peripatein said:

Homework Statement


Will the moment of inertia of a two dimensional rectangle (with sides a, b) whose axis is parallel to one of its sides and passes through its center of mass, be (1/12)M(a2+b2)?
No. If the axis is, say, the y axis, think of the lamina as a set of parallel thin strips in the x direction. They'll all have the same moment. I think the formula you quoted would be right for an axis perpendicular to the lamina.
 
But then wouldn't I be getting a moment of inertia equal to (Ma^2)/12 (supposing axis is parallel to a)?
 
And what's wrong with that?
 
It's not that something's wrong with that, simply that it seemed a bit strange it would not depend on the other side too.
 
peripatein said:
It's not that something's wrong with that, simply that it seemed a bit strange it would not depend on the other side too.
That's why I said to think of it as parallel strips across the axis. Adding more only increases the moment in proportion to the mass.
 

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