Couple (mechanics)

In mechanics, a couple is a system of forces with a resultant (a.k.a. net or sum) moment but no resultant force.[1]

A better term is force couple or pure moment. Its effect is to create rotation without translation. In rigid body mechanics, force couples are free vectors, meaning their effects on a body are independent of the point of application.

The resultant moment of a couple is called a torque. This is not to be confused with the term torque as it is used in physics, where it is merely a synonym of moment.[2] Instead, torque is a special case of moment. Torque has special properties that moment does not have, in particular the property of being independent of reference point, as described below.


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