1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Parrelle Axis Theorem Help

  1. Feb 18, 2008 #1
    Im having a hard time getting my head around this, any help would be much appreciated.

    1. The problem statement, all variables and given/known data

    Determine the position of the centroid and calculate the second moment of area about a horizontal axis passing through the centroid for the following sections shown. Attached is the image of the shape, including dimensions.

    2. Relevant equations

    A x Y(bar) = (A1 x Y1) + (A2 x Y2)
    IX = Ix + Ah(squared) [Not sure if this equation is correct]

    3. The attempt at a solution

    I know Y(bar) to equal 40mm for the attached shape. However i dont know how to get from the y(bar) to the position of the centriod. The answer should be 862000.0mm, i just dont know how to get there, everything i try comes up with a different result.

    Attached Files:

  2. jcsd
  3. Feb 19, 2008 #2


    User Avatar
    Science Advisor

    Well, you have me confused! (Not all that difficult.) In most textbooks, "Y(bar)" ([itex]\overline{Y}[/tex]) means the y-component of centroid. I, frankly, don't see how you could have gotten 40 mm. That's only a little bit above the bottom line. You do understand, don't you, that the "centroid" of a figure is the geometric center? If this, very symmetric, figure goes from 20 mm at the bottom to 120 mm at the top, 10mm on the left to 80 on the right, where do you think center is?
    Last edited by a moderator: Feb 19, 2008
  4. Feb 19, 2008 #3
    Yeah [PLAIN]https://www.physicsforums.com/latex_images/16/1615993-0.png [Broken] is what i meant, i couldnt find the symbol. My diagram might not be clear, but the height is 80mm and considering its symetric in the x and y direction i thought [PLAIN]https://www.physicsforums.com/latex_images/16/1615993-0.png [Broken] = 1/2 total height?

    Is that not right?
    Last edited by a moderator: May 3, 2017
  5. Feb 26, 2008 #4
    Bump. On my hands and knees here guys :S
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook