Sorry, I meant to title it "Basic statics question on bending moment equation." Oh well. 1. The problem statement, all variables and given/known data Problem F7-7 http://www.scribd.com/doc/94480961/Chapter-7-Fundamental-Problems [Broken] 2. Relevant equations Summation of the forces in y, summation of the moments 3. The attempt at a solution I calculated the reaction at A, then found the shear force equation. ƩF_y = 0 = Ay - 6kN , so Ay = 6 kN The answer to the moment equation is supposed to be: ƩM = 0 = M + 18 -6x So M = 6x -18 I am particularly interested in why the M is positive in the beginning part of the moment equation. If someone could provide an explanation of the part along with a picture of the free-body diagram that's needed to make the moment equation, that would help out a lot. I am trying to understand chapter 7 but the more I read, the more confused I become.