## What is torque / torsion

When a force acts on a structure the two primary effects that it has is under the direct effect of the force and the twisting effect of the force.

The twisting effect of the force measured at a point depends on the magnitude of the force and the distance from the line of action of the force to the point where torsion is being considered.

Thus in simple words torque or torsion is the twisting effect produced by a force.

## Torque formula

The equation for torque is given as the product of force and the distance of line of action from the point considered for torsion or torque.

The triplet formula for torsion is given as follows:

\frac{\mathrm{T}}{\mathrm{J}}=\frac{\tau}{\mathrm{R}}=\frac{\mathrm{G} \theta}{\mathrm{L}}where,

T = Torque or Torsion

J = Polar moment of inertia

G = Shear modulus or modulus of rigidity.

Theta = Twist angle

L = Length of the shaft

Tau = Shear stress at a radial distance of ‘R’.

The SI unit of torque is depended on the SI unit of force which is Newton (N) and the SI unit for distance which is meter (m). Thus the SI unit for torque is Nm

## Torsional Rigidity

The term GJ is called as torsional rigidity and is used to determine how much torque a particular shaft can resist.

It is also defined as the Torque per unit angle of twist per length of the shaft.

GJ = T/ (Theta/L)

## Torque dimensional formula

The dimensional formula for torque depends on dimensional formula for force which is \left[\mathrm{M} \mathrm{L} \mathrm{~T}^{-2}\right] and dimensional formula of length which is [L], thus the dimensional formula for torque is given as:- \left[\mathrm{M} \mathrm{L}^{2} \mathrm{~T}^{-2}\right]