Torque is the rotational equivalent of force. To move an object in a straight line, or to deflect a moving object, apply a force. Similarly, to spin an object, or to alter its rotation, apply a torque.

Definition of Torque:   τ = r × F

The torque magnitude is r F sin θ. Here r is measured from the axis of rotation to the line of the force, and θ is the angle between r and F.

The torque direction is given by the right-hand rule. With your right hand, point your fingers in the direction of r and curl them into the direction of F. Your thumb points in the direction of the torque.

Note that the torque is:

• zero when r and F are parallel or in opposite directions;
• maximum when r and F are perpendicular.