  While optics and mechanics are two distinct branches of physics, they are
connected. It is well known that geometrical/ray treatment of light has direct
analogies to mechanical descriptions of particle motion. However, connections
between coherence wave optics and classical mechanics are rarely reported. Here
we explore links of the two for an arbitrary light field by performing a
quantitative analysis of two optical coherence properties: polarization and
entanglement (implied by a wave picture of light due to Huygens and Fresnel). A
universal complementary identity relation is obtained. More surprisingly,
optical polarization, entanglement, and their identity relation are shown to be
quantitatively associated with mechanical concepts of center of mass and moment
of inertia through the Huygens-Steiner theorem for rigid body rotation. The
obtained result bridges coherence wave optics and classical mechanics through
the two theories of Huygens.
