Why isn’t the Earth perfectly spherical?
The Earth’s rotation creates an outward force perpendicular to its rotation axis which, crucially, is proportional to the distance from that axis. Hence, the highest force is felt at the Earth’s equator, while the force is zero at the poles. Since the Earth is not perfectly solid throughout, this force results in the Earth being ‘squashed’ into a slightly flattened sphere. The effect is quite small. The diameter at the poles is about 12,714km and at the equator is about 12,756km; hence the amount of flattening (or ‘oblateness’) is only about 0.3 per cent. However, this equatorial bulge (42km) is about twice the distance from the top of Mount Everest to the deepest part of the ocean. AGu
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