To satisfy the condition that there should not be translatory motion of the body subjected to coplanar forces, in this case also the following two conditions are to be satisfied:
If the condition ΣMA = 0 is satisfied, we can conclude that the resultant R should be a force passing through A. If ΣMB = 0 is satisfied, the line of action of the resultant passes through B, i.e., AB is the line of action. Now, if ΣMC = 0 is also satisfied, the resultant should be zero since the line of action of the resultant (line AB) cannot pass through C also. Thus if A, B, C are not collinear points, the following conditions are necessary and sufficient conditions of equilibrium.
Three problems are solved in this article. The problem of finding the reactions at supports of beams and trusses also fall under this categories. But these problems are solved in the chapters analysis of beams and trusses.
