Moment of Inertia of a Sphere derivation?

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Discussion Overview

The discussion revolves around the derivation of the moment of inertia of a sphere, specifically seeking methods to achieve this without relying on the moment of inertia of a cylinder. Participants are exploring theoretical approaches and integration techniques related to this concept.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant asks if it is possible to derive the moment of inertia of a sphere from scratch without using the moment of inertia of a cylinder.
  • Another participant suggests integrating over the sphere to obtain the moment of inertia.
  • A request for clarification on how to perform the integration is made by a participant.
  • There is a mention of needing to know the expression for the moment of inertia for arbitrary objects to proceed with the integration.
  • One participant expresses uncertainty about how to properly set up the equation for integration.
  • A link is provided to a resource on spherical coordinates, which may assist in the integration process.
  • A later post asserts that it is indeed possible to derive the moment of inertia of a sphere from scratch and references an article that outlines a general method for calculating mass and moments of inertia for various bodies.

Areas of Agreement / Disagreement

Participants express differing levels of familiarity with the integration process and the derivation methods. There is no consensus on a specific approach to derive the moment of inertia of a sphere, and multiple viewpoints on how to proceed remain present.

Contextual Notes

Some participants indicate uncertainty regarding the setup of equations necessary for integration, and there may be dependencies on definitions and assumptions that are not fully articulated in the discussion.

Timothy S
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Hi,

Is there a way to derive the moment of inertia of a sphere without using the M of I of a cylinder? In other words, is it possible to find a sphere's from scratch? Please include a derivation in your answer, unless there isn't one of course.
 
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Why don't you just integrate over the sphere to get it?
 
can you explain to me how to do that?
 
Do you know the expression for the moment of inertia for an arbitrary object?
 
I do, but I don't know how to properly set the equation so that I can integrate.
 
Timothy S said:
Hi,

Is there a way to derive the moment of inertia of a sphere without using the M of I of a cylinder? In other words, is it possible to find a sphere's from scratch? Please include a derivation in your answer, unless there isn't one of course.
Of course there is a way to derive the MOI of a sphere or any other body from scratch. Do you think we make these things up to torture college freshmen?

This article:

http://www.solitaryroad.com/c375.html

contains the general method for calculating mass, the location of centroids, and the mass moment of inertia for a general body.

See Section II - Moments of inertia of masses.
 

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