In
mechanics, a
couple is a system of
forces with a resultant (a.k.a. net or sum)
moment but no resultant force. A better term is
force couple or
pure moment. Its effect is to create
rotation without
translation, or more generally without any acceleration of the
centre of mass. In
rigid body mechanics, force couples are
free vectors, meaning their effects on a body are independent of the point of application.