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Difference Between Torque and Bending Moment

Torque is a rotational equivalent of a linear force that causes the twisting of a section about an axis. A bending moment as the name suggests is the moment that causes a section to bend. In this blog, we will see each of the terms in detail.


Torque


Torque is a type of moment that causes the twisting of a section. It mostly acts perpendicular to a section. Torque is given as the product of force and perpendicular distance (radius) about which the force acts. Transmission shafts are often subjected to torque as they transmit power by rotation.


Torque = Force (F) * Radius (r)

Torque
Torque

Bending Moment


The bending moment causes the bending of the section. It mostly acts along the plane of the section. The bending moment is given as the product of force and the perpendicular distance between the point (where the bending moment is required) and the point of action of force.


Bending moment = Force (F) * Perpendicular distance between the point and the point of action of force

Bending moment in a section
Bending moment in a section

Difference Between Torque and Bending Moment


From the definition and formulas, it is understood that both torque and bending moments are some kinds of moments. They even have the same unit as Nm. What differentiates a bending moment from a torque is the axis about which moment is applied.


  • If the moment is applied about the longitudinal axis - it causes twisting of the section - then it is called a Torque

  • If the moment is applied about the transverse axis - it causes bending of the section - then it is called a Bending moment


Another distinguishing factor is the stresses caused by torque and bending moment.


  • Due to Torque, predominantly shear stress is induced

  • Due to the bending moment, predominantly normal stress is induced



Hope the key difference between torque and bending moment is understood. This is a short blog but if you want us to cover long boring topics in an interesting way let us know in the form below.




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