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Freebody/Force Diagrams

  1. Jun 12, 2008 #1
    Hello all. I had a question about freebody diagrams. I know how to draw them and solve for forces/acceleration/mass/friction but one thing I was confused about is when you list summation of forces in either X or Y direction if there's a specific order to list them in, or if it matters. I know to list forces like Force of tension - Force friction =max but where would the X component of gravity fit in? I know the +/- symbols account for direction of the vector but does it matter in which order the forces are put in? Thanks for any and all help in advance! Hoping for a quick reply.
  2. jcsd
  3. Jun 12, 2008 #2
    real numbers are associative and commutative (a mathematical property meaning it doesn't matter in what order you add/subtract them). 1 + 2 = 3 as does 2 +1
    Last edited: Jun 12, 2008
  4. Jun 12, 2008 #3

    Doc Al

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    Order doesn't matter (as long as you have the signs right). Addition is commutative: A + B = B + A.

    (Does gravity have a horizontal component? :wink:)
  5. Jun 12, 2008 #4
    Thanks guys! I had a feeling I wasn't just getting lucky each time :D.

    It sure does when you turn your paper theta degrees, haha.

    I look forward to posting more and contributing, as I was a lurker before this. You guys are very helpful and damn fast! Again, thanks guys.
  6. Jun 12, 2008 #5


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    I'd suggest that you first write the "SUM of the Forces" vectorially.
    [tex]\vec T+ \vec W+\vec f[/tex] (order not important), then choose your axes, then break into components...
    [tex] T_x+ W_x+ f_x[/tex] (keep order for bookkeeping)
    [tex] T_y+ W_y+f_y[/tex],
    then write "0" or the appropriate signed quantities for certain components.
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