Editing Coriolis force (section)

===Direction of Coriolis force for simple cases===

As the Coriolis force is proportional to a [[cross product]] of two vectors, it is perpendicular to both vectors, in this case the object's velocity and the frame's rotation vector. It therefore follows that:
* if the velocity is parallel to the rotation axis, the Coriolis force is zero. For example, on Earth, this situation occurs for a body at the equator moving north or south relative to the Earth's surface. (At any latitude other than the equator, however, the north–south motion would have a component perpendicular to the rotation axis and a force specified by the ''inward'' or ''outward'' cases mentioned below).
* if the velocity is straight inward to the axis, the Coriolis force is in the direction of local rotation. For example, on Earth, this situation occurs for a body at the equator falling downward, as in the Dechales illustration above, where the falling ball travels further to the east than does the tower. Note also that heading north in the northern hemisphere would have a velocity component toward the rotation axis, resulting in a Coriolis force to the east (more pronounced the further north one is).
* if the velocity is straight outward from the axis, the Coriolis force is against the direction of local rotation. In the tower example, a ball launched upward would move toward the west.
* if the velocity is in the direction of rotation, the Coriolis force is outward from the axis. For example, on Earth, this situation occurs for a body at the equator moving east relative to Earth's surface. It would move upward as seen by an observer on the surface. This effect (see Eötvös effect below) was discussed by Galileo Galilei in 1632 and by Riccioli in 1651.<ref name=Graney2015>{{cite book| last=Graney|first=Christopher M.| title=Setting Aside All Authority: Giovanni Battista Riccioli and the Science Against Copernicus in the Age of Galileo| year=2015|publisher=University of Notre Dame Press|location=Notre Dame, IN| pages=115–125| url=https://books.google.com/books?id=6r_nrQEACAAJ| isbn=9780268029883}}</ref>
* if the velocity is against the direction of rotation, the Coriolis force is inward to the axis. For example, on Earth, this situation occurs for a body at the equator moving west, which would deflect downward as seen by an observer.