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Homework Help: Derivation of formula of centroid

  1. Nov 23, 2015 #1
    1. The problem statement, all variables and given/known data
    what is y ′and y bar ? why y ′ is changed to y bar ? why are they = 0 ?

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Nov 23, 2015 #2
    The middle integral is zero because y' is measured w.r.t. to the centroid so that
    each value of y' dA is cancelled by -y' dA by definition of a centroid or in other
    words y-bar = zero when measured from the centroid.
    Also, since y' is measured from the centroid then the integral of y'^2 dA is just
    the moment of inertia about the center of mass which is Ix.
  4. Nov 23, 2015 #3
    in the first integral , the
    in the first integral , the y prime is squared , so they dont cancel out each other?
  5. Nov 23, 2015 #4


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    Staff Emeritus
    Science Advisor
    Homework Helper

    When have you squared a real number and it came out negative?
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