An Explication of the Coriolis Effect

The object of this note is to provide an interpretation of how motion on the rotating earth is affected by that rotation. The physical principles to be used are extremely well known, but as far as I know, have not been applied to this problem in precisely this style, a style designed to avoid the solution of differential equations. In spite of its long history, the subject is very much alive, especially in a pedagogical context (Stommel and Moore 1989; Duran 1993). Persson (1998) provides many references and a historical perspective. Two examples are discussed here, inertia circle motion and geostrophic flow. It is suggested that the results might provide a simple physical understanding to supplement the elementary manipulations in the conventional derivation of the Coriolis force, which, according to Persson (1998) and Stommel and Moore (1989), remain a mystery to many. Inertia circle motion is the idealized behavior of a particle that is confined to horizontal motion on the earth and, when viewed in a framework fixed to the rotating earth, has its horizontal displacements subject only to the Coriolis force. This makes it a simple example from which to understand the Coriolis effect on motion. For horizontal motion, that force is equal to the product of the speed, C, and the Coriolis parameter, f: