Difference Between Torque and Couple

Torque vs Couple

Moment, torque and couple are concepts often encountered by students studying physics and these are also terms that are often confused by them. There are similarities between a torque and a couple but there are striking differences also that will be explained in this article.

Torque is a special kind of force that has the capacity to rotate an object about an axis. While a force is described as a push or a pull, it is better to think of torques as a twist. Daily life examples of a torque are when you use your hands to turn the steering of your car or when you try to unscrew a nut using a wrench. Simply speaking, a torque is a turning force. You apply force on the wrench which opens the screw. However, students get confused as this fore is called a torque when they study physics at school but the same force is referred to as moment while studying it in mechanical engineering.

In a special case when applied force vectors add to zero, then the force is called a couple and their moment is called a torque. Thus the rotational force that produces no moment is called a couple. Couple is also referred to as a pure moment. The most basic kind of couple takes place when two equal but opposite forces act on a body whose lines of forces do not coincide. The SI unit of a couple is Newton-meter.

Torque vs Couple • The turning effect produced by a force on a body is called torque. It is calculated as force multiplied by perpendicular distance. • A couple is a special case when there are two equal but opposite forces acting on a body that rotate it.