## Area moment of inertia and second moment of inertia

Hi PFians

What is the significance of area moment of inertia and second moment of inertia?
Well, I know that it signifies resistance to bending but how can you explain practically.

I mean if we see mass moment of inertia, we can say that it tells us how mass is distributed in 3d about an axis of rotation which effects the rotational acceleration. This way can you explain the above two, physically, so that it becomes clear in my mind rather than just knowing the formula for both.
Thanx

BTW merry christmas to all of you.
Merry Merry I ring the bells,
Make merry the christmas tells!
-R
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 Recognitions: Science Advisor Well, they are both one and the same. The exact same thing you mentioned for rotation is the same for bending. The larger the MOI, the greater the distribution of mass about that axis. I think of a flexible, metal ruler in this case. Your own intuition should tell you that the ruler should be easier to bend in the orientation that has the smallest thickness. Put the rectangle on end and see how difficult it is to bend.

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