Image:Forces oblate spheroid.gif
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Forces_oblate_spheroid.gif (9KB, MIME type: image/gif)
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Description:
This sequence of three images shows the forces that are at play on a rotating planet such as Earth. Because of its rotation, the Earth is not spherical in shape, it is an oblate spheriod. The force of gravity is directed towards the center of the Earth. The normal force is perpendicular to the local surface. Except on the poles and on the Equator the two forces are not exactly in opposite direction, so there is a resultant force, that acts in poleward direction. The laws of motion imply that this poleward force is at every latitude precisely the amount of centripetal force that is necessary to maintain an even thickness of the atmospheric layer. The solid Earth is ductile. If the shape of the solid Earth would not be close to an oblate spheroid, then the shear stress would deform the solid Earth over a period of millions of years until the shear stresses are resolved.
Created: 12 January 2006
Author: Cleonis
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