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.