CBSE Class 11-science Answered

Couple:

Imagine a sailor turning the wheel of a ship with his two hands. Here he applies two forces which are equal and opposite in direction (let us suppose), as shown in the figure below.

The arrows denote the direction of forces exerted by the sailor. The action of applying of two equal and opposite forces forms a couple. It is easy to understand as couple means two. As the coupling force turns the wheel it produces torque.

So, Torque is a rotational force which happens as a result of the couple or couple produces torque.

The same principle applies when we open a tap by applying a coupling force with our fingers (which turns the tap).

Torque and moment:

• Torque is a movement force. Moment is a static force. Torque is often presented as Nm/revolution and moment is typically presented as Nm. The words "torque" and "moment" (of force) mean the same.

From this equation, it is clear that if we want to complete the task using less force, we have to increase the distance from the pivot.

In contrast, when a car driver turns a steering wheel, he exerts two equal and opposite forces on the steering. These forces form a couple and the turning effect of this couple is the sum of the moment of the two forces. The moment of a couple is called Torque.

Torque= Force*Perpendicular distance between the two perpendicular forces

In common practice, Torque and moment are used interchangeably. Torque, or the moment of a force is its ability to rotate an object about an axis.