There is a bar AB. A is fixed and a force F is applied at B perpendicular to the bar. The result of this can be computed by taking equal and opposite forces acting at A perpendicular to the bar (therefore they cancel out and the net force at A is zero, hence this is equivalent to the initial condition). The opposing forces at A & B form a couple, producing rotation, and the other force left at A causes a reaction. So this is the net effect of the force at B. My question is : 1. What is happening actually to cause this effect, i.e if we were not to apply equal and opposite forces at A, then how else would we arrive at this conclusion/ result? Is it at the moleculer or lattice level, due to the bonding etc. Can somebody explain the real mechanism? 2. If at A the "fixed" constraint, then what would happen to the bar and at A? Thanks.