ABSTRACT
Note that only one equation from the FBD of joint 1 is needed to find the remaining unknown of F1. The second equilibrium equation is identically satisfied. The two equilibrium equations from the FBD of joint 2 would also be identically satisfied. These three “unused” equations can serve as a “check” for the accuracy of the computation. We need not use these three joint equations because we have already used three equations from the equilibrium of the whole structure at the beginning of the solution process. This fact also points to an important point: There are no more than six independent equilibrium equations. Any additional equations are not “independent” from the six equations we just used, because they can be derived from the linear combination of the six equations. Any six “independent” equations are equally valid. The selection of which six equations to use is a matter of preference and we always select those equations that give us the easiest way of getting the answer to the unknown forces as we just did.
