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B Combining Rotational Inertias

  1. Apr 17, 2016 #1
    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?
     
  2. jcsd
  3. Apr 17, 2016 #2

    Doc Al

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    Staff: Mentor

    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.)
     
  4. Apr 17, 2016 #3
    probably should have specified, the z axis, or the axis perpendicular to the plane. the axis of choice is the blue COM, and I dont know how to find the moment of inertia of each shape except with central axes (I dont know much in the world of rotational inertia)
     
  5. Apr 18, 2016 #4
    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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