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Can anyone explain why the moment of inertia for a tubular column in that textbook is like so? (take a look at the attachments). It should be (I = MR^2), as far as I know.
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Can you derive it?I think they are assuming the material has uniform mass density. So the mass is proportional to the area but then they are off by factor of 2.
For polar area moment of inertia, yes, but for Ix , or Iy, the approximation should be as given.but then they are off by factor of 2.
For a ring,Can you derive it?