# Torsional Stiffness

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

## Torsional Stiffness FORMULA

$$\large{ k = \frac{ G \; J }{ l } }$$
Symbol English Metric
$$\large{ k }$$ = torsional stiffness  $$\large{\frac{lbf-ft}{deg}}$$ $$\large{\frac{N-m}{rad}}$$
$$\large{ l }$$ = length $$\large{in}$$ $$\large{mm}$$
$$\large{ G }$$ = shear modulus $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$
$$\large{ J }$$ = torsion constant (polar momentum of inertia) $$\large{in^4}$$ $$\large{mm^4}$$