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Suppose the Earth's rotation slowed for some reason. Would the lack of centrifugal force cause us to feel heavier than normal?

Likewise, if Earth's rotation increased, would we feel lighter as centrifugal force lifts us from the ground?

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2 Answers 2

The centrifugal force at the equator is only 1/289 of normal gravity, or 0.35%. That's too small to be perceived.

http://books.google.com/?id=mE4GAQAAIAAJ&pg=PA358&lpg=PA358

It gradually diminishes as you move away from the equator, and becomes zero at the poles.

In any case, if Earth stopped rotating, the added weight at the equator would be the least of your worries. There would be major perturbations in terms of weather, etc, that would amount to global catastrophe.

Likewise, if Earth's rotation increased, would we feel lighter as centrifugal force lifts us from the ground?

In theory, yes. But the rotation increase would have to be huge. Again, in that case, there would be other, much bigger effects, that would be much more important than your loss of weight. E.g. the whole planet would bulge at the equator and become more flat at the poles, with incalculable effects on plate tectonics, weather, etc.

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I find myself wondering if the effects on the Earth's magnetic field might not even be worse than the changes in the weather...hmm... –  Shinrai Apr 30 at 3:37
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If the rotation would stop, we would feel an additional gravity of $0.034 \mbox{ m}/\mbox{s}^2$, or about 0.35%, at the equator, (incorrectly) assuming the shape of Earth isn't changed by the changing rotation.

The centrifugal acceleration is $v^2/r$, with $v=465.1 \mbox{ m}/\mbox{s},$ and $r=6378100 \mbox{ m}.$

With shorter rotation period, the other way, as you say.

Polar regions wouldn't be affected, with the exception, that the ellipsoid of Earth would change due to changing rotation period. Respecting this, gravity would increase at the poles with faster rotation, since the poles would get closer to Earth's center. In equatorial regions the change of surface gravity would be affected more than in the simplified calculation above. In contrast to the poles, faster rotation would reduce surface gravity more than just by the centrifugal force.

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