Torsional Force

By BYJU'S Exam Prep

Updated on: September 25th, 2023

If a torsional load is applied to a material, it will create shear stress, which induces torsional force. If this force is large enough, it can cause the material to twist. This twisting force is called the torsional force.

Torsional force is used in several medical and general applications for performing various complex tasks. For example, immobilization devices, hospital beds, wheelchairs, etc. In these applications, springs are used, which store torsional force for their operation. Let us check more about torsional force in the upcoming sections.

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What is Torsional Force?

Torsional force is a force that is applied by a torque. A torsion force is a load applied to a material through torque. Applied torque creates shear stress. If a torsion force is large enough, it can cause a material to turn into a twisting motion during elastic and plastic deformation.

The torsional force applied to the body affects its rotational motion and creates a twisting effect on the body. It tends to induce torsional stress in the body. The torsional capacity of the section will depend on the polar moment of inertia of the cross-section and radial distance from the center.


Torsional Force Unit

As we know, torsional force is also a force that causes a twisting effect on the cross-section. So, the unit of this force is also Newton (N). While torsion is the twisting moment for the cross-section, it has the unit same as the unit of the moment, N-m. The twisting force induces torsional stresses, which is stress, so the unit of torsional stress will be the N/m2 or pascal.

  • SI unit of torsional force: Newton (N)
  • SI unit of torsional moment: N-m
  • SI unit of torsional stress: N/m2 or pascal

What is Torsional Moment?

A torsional moment is produced by a torsional force acting on the body. A torsional moment is the capacity of the body against its twisting motion. The torsional moment can be expressed by torsional force multiplied by a lever arm.

A torsional moment is a moment that is produced by a twisting force applied to the body along the transverse axis of the body. While forces along the axis produce uniform stress over the cross-section of the body, twisting force creates torsional stress over the cross-section, which is triangular.


Effect of Torsion in Beam

Torsion in beams comes into the picture due to the effect of transverse load (i.e., shear force) in the beam. It reduces the strength of the beam; hence, the safe design effect of torsion needs to be considered while designing the beam. In beams, the effect of torsion is considered in the form of shear force and bending moment.

As we know that torsion is an important parameter in designing civil engineering structures. In the case of designing the beam, some effect of torsion is included in the design for the bending moment as well as some effect is being considered along with the Shear force.

Difference Between Torsion and Bending

Torsion and bending both are the moment capacity of a section, But torsion is the twisting moment, and bending moment is the longitudinal moment. The same units are used for both the bending moment and the Torque moment. The bending moment causes the section to bend, and the Torque moment causes the section to twist. 

Torsion is the moment that acts about the transverse axis of the body, and bending is the moment that acts about the longitudinal axis of the body. Bending moment is caused by the force which acts perpendicular to the longitudinal axis, while torque is caused by the force which acts parallel to the transverse axis.


Torsion Formula

The torsional formula is an equation that relates the torsional moment, torsional shear stress, and other torsional parameters. With the help of the torsional equation, designing shafts and other torsional elements must be done.


Torsional Force Examples

Torsional force is an important concept of physics that is mostly seen in the case of the rotation of bodies. Torsion also plays an important role in designing civil engineering structures like beams and columns. Here some useful examples of torsional force are listed below.

  • Opening or closing a bottle
  • Tightening or losing the screw
  • Movement of the needle of the clock
  • Fitting of ceiling light
  • Medical equipment
  • Radio tuning

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