The Hamiltonian of a free particle in a rotating frame is given by H=H0ωJ,H = H_0 - \omega \cdot J, where H0H_0 is the Hamiltonian in the non-rotating frame, ω\omega is the angular velocity of the frame and JJ is the angular momentum of the particle. This relation is too beautiful to be a coincidence. Does it hold for arbitrary systems with rotational invariance? Is a more general statement possible?