For the forces in the truss segments, how do I knowwhich direction they go based

Question

For the forces in the truss segments, how do I knowwhich direction they go based on which direction theforce is being applied on the joint they all share? Someproblems(6-20) creates tension when pushing down. I'massuming it's because the truss is on a wall. This problemshows a force that's pushing down creating compression. If I guess wrong on which way the force goes in asegment, will it change the answer to the problem?(Like having anopposite sign?) For the forces in the truss segments, how do I knowwhich direction they go based on which direction theforce is being applied on the joint they all share? Someproblems(6-20) creates tension when pushing down. I'massuming it's because the truss is on a wall. This problemshows a force that's pushing down creating compression. If I guess wrong on which way the force goes in asegment, will it change the answer to the problem?(Like having anopposite sign?)

Explanation / Answer

The direction that you draw won't matter, as long as you areconsistent. You may get a negative number for the force, which justmeans that the force points in the direction opposite that you havedrawn. Personally, I think it's less confusing if you just always draw thearrows away from the joint (the members in tension) so that youalways know what a +force and a -force is without looking at yourdrawing again.

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