Mechanics maths question- centre of mass

Discussion in 'Community Discussion' started by yorkshire, Jan 10, 2010.

  1. yorkshire macrumors 6502a

    yorkshire

    Joined:
    May 18, 2008
    Location:
    UK
    #1
    Right, so I have a mechanics module tomorrow morning, and I'm almost there, the only thing stumping me is the centre of mass of a uniform semicircular lamina.
    I have the formula for a sector of a circle, which is

    2r sin(angle)
    sin (angle)
    (r is radius)

    Now when it's a semicircle then the angle would be ∏ radians, but sin(∏) is 0 therefore this formula isn't going to work. Am I missing something here?

    I did google this and the answer I saw is
    4r
    3p


    Yet nowhere I saw this did they say what p was. Is it short for pi?

    Thanks for any help, this is getting me stressed out!
     
  2. miles01110 macrumors Core

    miles01110

    Joined:
    Jul 24, 2006
    Location:
    The Ivory Tower (I'm not coming down)
    #2
    Yes, the "p" is pi. It's not a particularly hard derivation; use polar coordinates.
     

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