An apparent force on moving particles in a noninertial coordinate system, that is, the Coriolis acceleration as seen in this (relative) system. Such a force is required if Newton's laws are to be applied in this system. In meteorology the Coriolis force per unit mass arises solely from the earth's rotation, and is equal to −2Ω × u, where Ω is the angular velocity of the earth and u is the (relative) velocity of the particle. Thus the Coriolis force acts as a deflecting force, normal to the velocity, to the right of the motion in the Northern Hemisphere and to the left in the Southern Hemisphere. It cannot alter the speed of the particle. The three components toward east, north, and zenith are, respectively, 2Ω (v sinφ − w cosφ), −2Ωu sinφ, and 2Ωu cosφ, where u, v, w are the component velocities and φ the latitude. Since the Coriolis force is in effect proportional to the speed, its importance in any given atmospheric motion may be judged from the representative speed and duration of the motion. See inertial force.