# Rotational stiffness ( depended on rigidity modulus of the material)

## Description

Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force. In general, stiffness is not the same as elastic modulus. Elastic modulus is a property of the constituent material; stiffness is a property of a structure. That is, the modulus is an intensive property of the material; stiffness, on the other hand, is an extensive property of the solid body dependent on the material and the shape and boundary conditions. For example, for an element in tension or compression the axial stiffness is depended on elastic modulus (or Young’s modulus), but the rotational stiffness is depended on the rigidity modulus of the material.

Related formulas## Variables

k | The rotational stiffness (N*m/rad) |

n | An integer depending on the boundary condition (=4 for fixed ends) (dimensionless) |

G | The rigidity modulus of the material (or shear modulus) (Pa) |

J | The second moment of area about the rotation axis (m^{4}/rad) |

L | Length of the element (m) |