On the Nature of the Cartesian Stiffness Matrix

the 6x6 stiffness matrix pertaining to a rigid body mounted on a linearly elastic suspension is revisited here, with the aim of shedding light on its nature via its associated eigenvalue problem. the discussion is based on screw theory and the eigenvalue problem thus arising, in its generalized form. the eigenvalues of the stiffness matrix are shown to occur in real, symmetric pairs, something that has been somehow overlooked in the literature, the product of each eigenvalue by the pitch of its corresponding eigenvector being shown to be non-negative.