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The Coriolis Force

Since the globe is rotating, any movement on the Northern hemisphere is diverted to the right, if we look at it from our own position on the ground. (In the southern hemisphere it is bent to the left). This apparent bending force is known as the Coriolis force. (Named after the French mathematician Gustave Gaspard Coriolis 1792-1843).



Side view


Top view locked camera


It may not be obvious to you that a particle moving on the northern hemisphere will be bending towards the right.
Consider this red cone moving southward in the direction of the tip of the cone.
The earth is spinning, while we watch the spectacle from a camera fixed in outer space. The cone is moving straight towards the south.
Below, we show the same image with the camera locked on to the globe.


Look at the same situation as seen from a point above the North Pole. We have fixed the camera, so that it rotates with the earth.
Watch closely, and you will notice that the red cone is veering in a curve towards the right as it moves. The reason why it is not following the direction in which the cone is pointing is, of course, that we as observers are rotating along with the globe.
Below, we show the same image,with the camera fixed in outer space, while the earth rotates.



Side view locked camera



Polar view



The Coriolis force is a visible phenomenon. Railroad tracks wear out faster on one side than the other. River beds are dug deeper on one side than the other. (Which side depends on which hemisphere we are in: In the Northern hemisphere moving particles are bent towards the right).
In the Northern hemisphere the wind tends to rotate counterclockwise (as seen from above) as it approaches a low pressure area. In the Southern hemisphere the wind rotates clockwise around low pressure areas.
On the next page we shall see how the Coriolis force affects the wind directions on the globe.

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© Copyright 1998 Soren Krohn. All rights reserved.
Updated 6 August 2000