The moment of inertia (I) for something is(adsbygoogle = window.adsbygoogle || []).push({});

[tex]I = \int y^2 dA[/tex]

How do I get dA for a circle?

Here is what dA should look like for moment of inertia:

http://myfiles.dyndns.org/pictures/circle_dA.png

dA in this case is NOT a derivation of [tex]A = \pi r^2[/tex]. Doing that will give you the polar moment of inertia (J) which is completely different.

If the integration was done correctly, the answer you get should be

[tex]I = \frac{\pi r^4}{4}[/tex]

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# DA of a circle

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