Inertial motion in the ocean is a free oscillation resulting from the Coriolis force acting on a moving water parcel with no other net horizontal force, and it occurs with an inertial period given by T = 2 x pi / f, where f = 2 x Omega x sin(latitude) is the Coriolis parameter and Omega is Earth's rotation rate (approximately 7.292 x 10^-5 rad/s); this period shortens toward the poles (where f is largest) and becomes infinite at the equator (where f = 0).