Imagine a mass moving on the surface of a rotating sphere. For instance, the mass could be parcel of air moving away from a high pressure region in the Earth’s atmosphere. It experiences a *Coriolis* force which, in the example shown in the figure below, pushes it from its original trajectory (orange) to move eastward (blue). Why does this happen, and how do we understand it intuitively?

Formally, the Coriolis force on is given by

(1)

where is the angular velocity of the rotating frame (Earth), and is the velocity of as seen by an observer on the Earth’s …