Freebody/Force Diagrams

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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.
 

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  • #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
 
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  • #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:)
 
  • #4
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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:)
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.
 
  • #5
robphy
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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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