# Difference between torque, moment and couple

I know the basics of them like Torque is force multiplied by the distance (from the point where there is no rotation like centre of gravity).
Couple acts because of two equal and opposite forces acting at a distance.
Moment is force multiplied by any distance from the body.
Turning moment is due to rotating force.
Bending moment is the force which cause the bending in rod(or such structure)

My question is whether torque and moment are similar or not, and what are their differences?
Torque is supposed to cause rotational motion but why the rotating body has turning moment, should not it be torque?
Can couple be called torque or moment?

• Related torque vs moment – Farcher Feb 18 '19 at 8:46
• It's worth noting that there is a distinction in the use (or lack thereof) of some of these terms between disciplines (I've observed this distinction most sharply between physics classes and engineering classes). – dmckee --- ex-moderator kitten Feb 18 '19 at 15:11
• Correction the term is Moment of Force as there are other types of moments, describing something multiplied by a moment arm distance, – John Alexiou Apr 8 '20 at 20:09

## 2 Answers

Torque is nothing but moment of force. Couple can be understood as two torques. Your understanding of terms is correct.

It depends on the context really, usually torque is used to describe the moment causing torsional stress (so rotating about the same axis as the shaft). While the two other orientations of moment are the bending moment causing normal stress. Couple is just a general term, since any two equal and opposite forces will cause a moment and zero resultant force.