Calculating Moment of Inertia for Combined Shapes

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  • Thread starter Thread starter Hayden Leete
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Discussion Overview

The discussion revolves around calculating the moment of inertia for a combined shape formed by gluing two planes together. Participants explore the methods for determining the moment of inertia, particularly focusing on the axis of rotation and the application of the parallel axis theorem.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about how to calculate the moment of inertia for a blue shape formed by combining two planes.
  • Another participant asks for clarification on the axis about which the moment of inertia should be calculated.
  • A suggestion is made to calculate the moment of inertia for each piece about the chosen axis and then sum them, mentioning the need for the parallel axis theorem.
  • The original poster later indicates that they have resolved their question through further research and expresses gratitude for the prompting response.

Areas of Agreement / Disagreement

The discussion does not reach a consensus on the method, but participants engage in clarifying questions and suggestions without resolving the initial inquiry.

Contextual Notes

The discussion lacks specific details on the shapes involved and the exact calculations required, as well as any assumptions made regarding mass distribution.

Hayden Leete
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https://scontent-syd1-1.xx.fbcdn.net/hphotos-xfl1/v/t34.0-12/13015003_664975026975127_933044449_n.png?oh=0259712996d9a6dde812f6d8886f56b9&oe=5715CA95
So, it's straight forward enough to calculate the moment of inertia of basic planes with evenly distributed mass, but if I were to say glue the red and green plane together, how would I find the moment of inertia of the blue shape?
 
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Hayden Leete said:
how would I find the moment of inertia of the blue shape?
About what axis?

You can find the moment of inertia of each piece about the axis of choice, then just add them. (You'll need the parallel axis theorem.)
 
Doc Al said:
About what axis?

You can find the moment of inertia of each piece about the axis of choice, then just add them. (You'll need the parallel axis theorem.)

probably should have specified, the z axis, or the axis perpendicular to the plane. the axis of choice is the blue COM, and I don't know how to find the moment of inertia of each shape except with central axes (I don't know much in the world of rotational inertia)
 
actually you know what, through more googling and researching stuffs, I've figured it out. I've been trying to find somewhere to explain this to me for a while now, but I didn't know exactly what to search for until your reply, so thanks for that :biggrin:
 

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