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Homework Help: Moment of Inertia formula

  1. Dec 13, 2006 #1

    Why is the end area of shell [tex]2\pi rdr[/tex]?

    Thanks in advance. :rolleyes:
  2. jcsd
  3. Dec 13, 2006 #2
    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.

    Last edited: Dec 13, 2006
  4. Dec 13, 2006 #3
    Oh, I got that! Thank you marlon! I am giving my first steps over integration. And congratulations for the award!!
  5. Dec 13, 2006 #4
    What award ?
    I just lost my guru badge to somebody else, lol.

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