## Section11.4Coriolis Force

In the Earth-based frame, there are two inertial forces, one directed away from the center of earth, and the other pointed in the plane perpendicular to the axis of rotation. The centrifugal force subtracts from the centrally directed force of gravitation, and is absorbed in the value for the acceleration due to gravity $g\text{.}$

Therefore, the inertial force that leads to unexpected effects in the Earth-based frame is the Coriolis force $\vec F_{cor}\text{.}$

\begin{equation*} \vec F_{cor} = -2m\vec \Omega\times \vec v. \end{equation*}

Therefore, a moving particle is deflected perpendicular to its direction of motion by the Coriolis force. As a result, northward moving particles in the northern hemisphere are deflected to the East while northward moving particles in the southern hemisphere are deflected to the West as illustrated in Figure 11.4.1. Note that the Coriolis force is perpendicular to the direction of velocity of the particle, as evident from the cross product.