Freebody/Force Diagrams

1. Jun 12, 2008

0338jw

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. Jun 12, 2008

maverick_starstrider

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
3. Jun 12, 2008

Staff: Mentor

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? )

4. Jun 12, 2008

0338jw

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. Jun 12, 2008

robphy

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

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