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Homework Help: Properties of the centroid of an area

  1. Jun 6, 2013 #1

    I am calculating the centroid of an area using this equation for composite bodies:

    sum(indivudual area times individual centroid)/sum(individual area) = distance from axis to centroid

    this is just y bar for a cross section that is symmetrical about the y axis

    I was under the impression that when you find y bar, then the areas of the cross section on either side of y bar would be equal, but this is not the case. Is this correct and if so why?

    I thought surely the centroid would mean there would be equal mass (or area in this case) on either side of it.
  2. jcsd
  3. Jun 6, 2013 #2


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    No, the centroid establishes the line about which the first moments of area are equal. That comes from the formula for finding the centroid of a composite figure.
  4. Jun 7, 2013 #3
    You may be interested to know that although the centroidal axis often is used for all sorts of things, the equal are axis has a use in the plastic design of steel cross-sections, when the sections are bent beyond their elastic limit.
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