Question

A couple produces motion in a straight line.
A. True
B. False

Answer 1

Hint:In order to solve this question we need to understand a translatory and rotatory motion. So a translatory motion is defined as motion confined to only in one dimension, also known as straight line motion, so a force acting on the body in a straight line would either push or pull the body in the same dimension. Whereas Rotatory motion is motion which is not confined in a plane, it can be two dimensional or three dimensional, in this motion either a force causing rotation known as torque or two equal and opposite force.

Complete answer:
A couple is defined as a twisting force which means it is a set of two opposite and equal parallel forces acting on the body along different lines of action of force which in result produce rotational motion. Couple forces do not create moments. It depends on magnitude and direction of force acting.

Also Couple forces are independent of the axis and it is mathematically defined as the product of magnitude of forces and the perpendicular distance between these forces. So a couple force produces only rotational motion not translational motion due to net force acting on the body is zero. Hence, a couple produces motion in a straight line is false.

Note:It should be remembered that couple forces are different from moment and they are not same. Couple forces not relaying on point of application for force whereas the moment is not. Couple depends on the axis of rotation and opposite forces whereas the moment only depends on two forces and it is independent of the axis of rotation. Stirring of wheel, turning of screwdriver are all real world examples of couple forces.