Torque vs Torsion
Torque and torsion are two very important concepts when it comes to the fields such as engineering, physics and motor mechanics. Torque and torsion are both the results of coupled forces. These concepts are extremely useful when designing structures and machinery, and must be accounted for because of the immense impact on the stability of the system. In this article, we are going to discuss the causes of torsion and torque, their significance, how to measure or calculate them, and their similarities and differences.
Torque
Torque is experienced in simple day to day activities such as turning a doorknob, fastening a bolt, turning the steering wheel, paddling a bicycle, or even turning your head. It must be noticed that in each and every one of these activities, the movements are circular or rotational movements. It can be shown that in every movement where a change in the angular momentum occurs, there is always a torque acting upon the object. A torque is generated by a pair of forces, similar in magnitude and opposite in direction and parallel to each other. These two forces are separated by a finite distance. In physics, the term moment also has the same meaning as torque. Torque is defined as the tendency of a force to rotate an object about an axis, a fulcrum or a pivot. A torque can also be provided using a single force acting at a distance r from the axis of rotation. The torque of such a system is equal to the cross product of the applied force and r. Torque is mathematically defined as the rate of change of angular momentum of and object. It can be clearly seen that this is compatible with the force – linear momentum relationship in linear movements. The torque is also equal to the product of the moment of inertia and the angular acceleration. Torque is a vector with the direction determined by the cross product of the force and distance. It is perpendicular to the plane of rotation.
Torsion
Torsion is experienced in day to day activities such as tightening a screw or twisting a cloth. Torsion is the deformation of objects due to a pair of equal and opposite torques. There can be torsion even if the net torque of the system is zero. If a single torque is applied to a fixed object, which cannot rotate in any direction freely there will always be another torque generated by the reactive forces on the fixed point. The amount of twisting due to an applied torque depends on the torsional rigidity of the system. The twist angle and the torque hold a linear relationship, where the torsional rigidity is the proportionality constant.
What is the difference between torque and torsion? – Torque is a measureable concept, whereas torsion is a concept, which is mathematically projected by the shear stress or the twist angle. – Torque requires at least one force and torsion requires at least two forces to happen. – Torque depends only on the magnitude, directions and the separation of the forces applied, while torsion depends on the torque, the type of material and the shape of the object.

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