Force-couple System

Force-couple System

• Force acting on an object produces translation and rotation of the object.

• The translational effects are represented by the magnitude and direction of the force whereas the rotational effects are represented by the moment of force. 

• Hence a force can be replaced by a force and couple as shown in Fig. 3.5.1. 

• Consider a force F acting at point A as shown in Fig. 3.5.1 (a).

• Add two forces of magnitudes at point O as shown in Fig. 3.5.1 (b) which are parallel to the force at A.

• The force at A and the force - at O form a couple with moment F.d about any point in the plane.

• Thus the force at A is replaced by a force at O and a couple of moment F•d as shown in Fig. 3.5.1 (c).

• This procedure can be extended to a system of non-concurrent forces which can be reduced to single resultant force and a couple.

• Conversely, a force-couple system can be combined to a single force acting at a distance 'd' from a given point O.