Question

define rigid body and point of action of force

Answer 1

A rigid body is defined as a body on which the distance between two points never changes whatever be the force applied on it.

Answer 2

A rigid body is a solid body in which deformation is mostly zero or so small it can be ignored only. The distance between two given points on a rigid body remains constant in time regardless of external forces applied to it. A rigid body is considered as a continuous distribution of mass.

The point of action of a force is a geometric representation of how the force is applied. It is the line through the point at which the force is applied in the same direction. The concept is for understanding the net effect of multiple forces applied to a body.