Couple (mechanics)

Couple is a term used in engineering mechanics.

The pair of forces is

• Of two equal forces,
• Which are parallel to each other but
• Act in the two opposite directions.

A force couple or two acting on a rigid body of the same size, anti -parallel forces, whose center of mass can not move. You can rotate the body only as a torque about its center of mass. The couple is thus a particular technical application of the general concept of mechanical torque. Another special feature is that the couple can be moved in its plane, without changing its effect on the body. Its torque (short: be the moment) is the product of the amount of the forces F (see figure) and the vertical distance a of the forces.

A couple is applied, for example on a two-armed wrench ( lug wrench ). If you go with both hands produces two equal, opposite forces on him, the screw only receives a torque. A protruding screw shaft is not subjected to shear and bending as with use of a simple wrench. The risk that the nut from the screw head bounces away as when using a single-arm socket wrench is small, as it is not tilted. If an extension between nut and armed socket wrench used, you have to prevent against hold the tilt with the second hand at the upper end of the extension. This external holding power is then the second power of the force couple.

The couple is in the computational treatment of the general power system (the lines of action of forces do not intersect at a common point ) on the rigid body useful. The forces can be summarized into a single force and a force couple.