6.32 stiffness. In a system in which friction and inertia are negligible during sinusoidal motion, quotient of force at a point by the in-phase displacement at the point, caused by the force. Unit, newton per meter (N/m).
Annotation 1 In the case of torsional stiffness, “force” and “displacement,” respectively, are replaced by “torque” and “angular displacement” and the unit is newton meter per radian (Nm/rad).
Annotation 2 See also 2.56.