Principle of moments
When dealing with problems involving a number of moments acting on a body the is not in equilibrium, the first step is to draw a sketch indicating the forces and eir distances from a fulcrum. It is customary to give a positive sign to anticlockwise moments and a negative
go to clockwise moments. The various moments are written down with appropriate
gins and are added algebraically. The sign of the answer will then give the direction
of the resultant moment. Example, A rod AE of negligible weight, 40 em long, is pivoted at a point D. eights of 1, 2, 3, and 4 N act on the rod as shown in Fig. 6.3.
Taking the forces acting from left to right, we have, measuring in metres
sum of moments = (1 x 0.30) – (3 x 0.20) + (2 x 0.10) – (4 x 0.10) = – 0.50.
Hence the resultant moment is 50 N m units acting in a clockwise direction.