# Torsion

## Description

In solid mechanics, torsion is the twisting of an object due to an applied torque. It is expressed in newton metres (N·m) or foot-pound force (ft·lbf). In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius.

Related formulas## Variables

T | applied torque or moment of torsion (N*m) |

J_{T} | torsion constant for the section. It is identical to the second moment of area Jzz for concentric circular tubes or round solid shafts only. For other shapes, J must be determined by other means. (m^{4}) |

r | distance between the rotational axis and the farthest point in the section (at the outer surface) (m) |

τ | maximum shear stress at the outer surface (N/m^{2}) |