Hi http://img686.imageshack.us/img686/2237/img0001zy.jpg In the 3rd figure on the right... I believe the x Force component (the sine term) should also be negative since it would point to the left, but the author has it as positive. Does it possibly have to do with even/odd function of sine? I wouldn't think so because sin(-x)= -sin(x) and I don't see any of that going on here. Agree? Thanks in advance.