Torque
Torque, a force that turns or tends to turn an object. The word torque comes from the Latin torquere, meaning to twist. When an object is not free to move—or when the torque is not of sufficient magnitude to rotate it—torque produces torsion, a twisting stress, in the object. The force used to swing open a door is an example of torque. Belts turned by electric motors exert torque on fans and other rotating devices. The shaft that drives an airplane propeller produces torque on the propeller.
Torque is calculated as force (measured in such units as pounds or newtons) multiplied by the length of the lever arm. The lever arm is the perpendicular from the axis of rotation of the body to the line in which the force acts. Torque is usually expressed in foot-pounds or newton-meters. Since torque depends on distance as well as force, a given force can be made to produce a larger torque by increasing the length of the lever arm.
Torque = F x L, where F is the force and L is the length of the lever arm.