What is Torque?

What is Torque?

Torque is a force that acts to cause rotation. Torque, also known as a moment or moment of force can be considered the rotational equivalent of linear force.


How does torque work?


Consider the left diagram above; a rod is pivoted at one end and a force applied at the other end. The force is applied at an angle to the rod as shown. Intuitively, it can be seen that the component of the force perpendicular to the rod (Ftan) will act to rotate the rod about its pivot; similarly, the radial component of the Force (Frad) will produce no turning effect – it is simply pulling the rod against its pivot.

Mathematically, we can also show this is the case; in the right diagram, the angle marked with the arc is conventionally called theta (0). The components of the force, F, can be calculated using trigonometry:

Ftan = F Sin (theta)

Frad = F Cos (theta)

If the force is applied completely perpendicular to the rod, then theta is 900. Sin (900) is 1 and Cos (900) is 0, so from the equations above,

Ftan = F

Frad = 0

The whole force is acting to create a turning moment or torque. Conversely, if the force is acting totally in the direction Frad then theta is zero. Sin (00) = 0, so, Ftan = 0 and there is no component of force acting to turn the rod.

Torque is defined as the force acting perpendicular multiplied by the distance of the force from a pivot point. Mathematically, from the diagrams above

T = F Sin (theta) x r and is measured in Nm (Newton metres).

Motors produce rotation and by definition a torsional force. This torque is turned into motion.

Want to find out more?

Read our articles on electric actuators, drives and motors to further your understanding, or use our electric actuator configurator to design and order a custom cylinder.