Chris,

Thank you for that thoughtful essay on the basis for structural
mechanics. It was well written and I agree with the principles you
outline. Although my structural mechanics may be a little rusty through
lack of use, I did study it to second year university level, and other
branches of mechanics to a higher level. I do consider myself to have a
good understanding of Newton's laws, free body diagrams, etc. In your
500+ words you have still not explained precisely why my free body
diagram is wrong. If it's wrong, I want to know why.

You left off the horizontal component of the tension in the "tension
member". I've said that at least three times now. Given the idealized
structure you created, it is simply where Newton takes us.

If you genuinely do not understand about the missing component, and are
close to a university, you might seek a tutor to help you with some
problems from a statics text. Find one for which you deviate from the
solution so you will have questions from the beginning. Many graduate
students are eager to pick up an hour's fee here or there, and won't
care that you are not enrolled as a student.

Bill