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Homework Help: Hollow square size

  1. Nov 26, 2015 #1
    1. The problem statement, all variables and given/known data
    I'am trying to make a simple machine which is to lift a display up and down. The construction mostly using hollow square.
    so far I got the weight of the display and the support is 25 Kg and I have this kind of construction.
    Beam.jpg
    if simplified become like this

    Beam 1.jpg
    2. Relevant equations
    which is the right moment happen in that construction?
    a.
    Beam 2.jpg
    b.
    Beam 3.jpg
    Is that necessary to calculate the moment?
    how do i get the right hollow square size?

    3. The attempt at a solution
     
  2. jcsd
  3. Nov 26, 2015 #2

    mfb

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    2017 Award

    Staff: Mentor

    Assuming your frame is rigid, both diagrams are equivalent.
     
  4. Nov 27, 2015 #3
    so calculating the moment is not necessary?
    is there any formula to get the right size of hollow square?
     
  5. Nov 28, 2015 #4

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    Which moment, necessary for what?
    Right size for what?
     
  6. Nov 28, 2015 #5

    CWatters

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    Science Advisor
    Homework Helper
    Gold Member

    Ask yourself what forces each tube is subject to. Perhaps start with the horizontal tube.
     
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