# Moment of Inertia formula

PSOA

Why is the end area of shell $$2\pi rdr$$?

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Why is the end area of shell $$2\pi rdr$$?

It's the area expressed in differential form. To acquire the correct formula, you need to calculate the integral with respect to r.

Intuitively, the differential form means this : to describe an infinitesimal small area, take the circumference 2 times pi times r and make it a bit thicker, expressed by the dr. Integrating over r means that you sum up the area of all this different, very thin, circumferences to get the total circular area.

marlon

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PSOA
Oh, I got that! Thank you marlon! I am giving my first steps over integration. And congratulations for the award!!

And congratulations for the award!!
What award ?
I just lost my guru badge to somebody else, lol.

marlon