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Homework Help: Help: Moment of inertia Ixx, Iyy, Izz, Ixy, Ixz, Iyz, etc?

  1. May 14, 2010 #1
    Help: Moment of inertia Ixx, Iyy, Izz, Ixy, Ixz, Iyz, etc??

    Hi all,

    Can someone help with a few equations?, i need to know the moment of inertia of a section.

    The section is a column which in the Z direction have 3m, on the X direction has 0.3m and on the Y direction has 0.6m.

    I know that Ixx on one direction is b*h^3/12 and for the other side Iyy is b^3*h/12... but what the equation for Izz and rest of the equations? (like Ixy, Ixz, Iyz, etc)

    Thank you

    -
    Diquan
     
  2. jcsd
  3. May 14, 2010 #2

    tiny-tim

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    Hi Diquan! Welcome to PF! :smile:

    (try using the X2 tag just above the Reply box :wink:)

    The moment of inertia of a body with constant cross-section depends only on the shape of the cross-section, so Izz wil be the same as for a rectangular plate 0.3m by 0.6m :smile:

    And mixed terms such as Ixy are zero if x y and z are principal axes of the body (and every axis of symmetry is a principal axis :wink:).
     
  4. May 15, 2010 #3
    Re: Help: Moment of inertia Ixx, Iyy, Izz, Ixy, Ixz, Iyz, etc??

    I think it would help you if you returned to the integral definitions: Ixx = integral y^2 da etc. Draw a diagram of the cross section, and you will be able to see how Ixx and Iyy relate to Izz
     
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