What would happen to life if the earth stood still? Would we float? Would that interfere with gravity?

Hasn't it been noted that the earth is slowing down?

"Hasn't it been noted that the earth is slowing down?" Yes, but the rotational slowing is so slight as to amount to about 15-20 microseconds (millionths of a second) per year. (Reference 1; Reference 2)

If the earth didn't rotate, gravity at the surface would be pretty much the same as it is now. At the equator the gravitational force would be slightly stronger (you would weigh slightly more) because (1) there would be no centrifugal force counteracting gravity and (2) the equatorial bulge would disappear, bringing everything slightly closer to the earth's center. Since the flip side of equatorial bulge is polar flattening, at the poles gravity would be slightly weaker because of slightly increased distance from the earth's center.

I haven't calculated the quantitative effect, but I should think it would so small you wouldn't even notice it. Climbing stairs would be just as tiring! Certainly you wouldn't float as if gravity were turned off!

As for the effects on life, that's way too complex for me to speculate. No day-night cycles, uneven heating of the surface by the sun, lack of tides, lack of atmospheric coriolis effect, altered dynamics of the planet's interior, etc., etc. The world would be a very different place indeed for many reasons.

Wow, thanks professor. Very good information.

No problem. Good question.

If memory serves me well, the earth would be a sphere if not for rotation. I wonder if it would eventually become a sphere if rotation stopped?

Despite the opinions of some on these boards, I was not here when the earth cooled, 'fuse. However I do believe that absent revolution about an axis, and persistence of heliocentric rotation, the temperature difference between the side facing and the side opposite the sun would produce more serious results than equatorial bulges. Strong prevailing winds and widespread population migrations would surely become popular,IMO n'est pas?

quote:

I wonder if it would eventually become a sphere if rotation stopped?

That's what I based my answer on. I think physics pretty much requires it for bodies above a certain mass. The force of gravity exceeds the strength of rocks and other solids to resist deformation to a sphere.

The erosion of mountains and filling in of valleys over geologic time is essentially the tendency toward sphericity.

Only lightweight bodies such as small asteroids can have weird shapes (peanut, potato, etc.) because gravity is too weak to matter.

If we stopped rotating, would the gravity of Sol pull the side facing the sun towards it?

Yes, but that would be a tidal effect arising from the difference in gravitational force between the near side and far side of Earth. Since the sun normally affects earth's tides about half as strongly as the moon does, you'd still see lunar tides but with lesser extremes. Average water level would now be a little different across the globe, however, being in effect a 'sun tide' frozen in place as a permanent deformation of earth, including continental crust and ocean floor. I suppose tectonic plates would continue to drift over geologic time, so L.A. might still arrive in Seattle some day , assuming that the ceased rotation hasn't fatally disrupted the convection of liquid magma in the mantle, on which the continental plates float about. I doubt the planet would tear itself apart -- say, a chunk of the planet breaking off and drifting sunward! After all, those same forces are already in play on the spinning earth and are not all that dramatic. The rise and fall of most tides amounts to something like one 10-millionth of the earth's radius.

The earth's orbit around the sun shouldn't change significantly with a non-spinning earth, provided that the earth's mass doesn't change, the average distance between sun and earth doesn't change, and the earth's orbital speed doesn't change. Those factors are not affected by tidal forces.

But these hypothetical scenarios are tricky. How exactly is the earth supposed to have stopped rotating? Where'd all the angular momentum go? Was it transferred to the moon? To the earth's solar orbit? It's a conserved quantity -- it has to go somewhere, but is that even relevant to this thought experiment?

Indeed, the original question was What would happen to life if the earth stood still? and perhaps I am hasty in taking "stand still" to mean "cease rotating". Perhaps it means completely standing still with respect to, say, the local cluster of galaxies. In this scenario, besides not rotating, the earth would no longer be orbiting the sun, either. So (depending on our motion relative to the sun) we'd either drift away forever from our life-giving sun to meet a cold, dark fate; or else we'd be drawn into the sun and quickly incinerated.

In the latter case the tidal forces might then become great enough to tear the planet apart as it approached impact (if that's the term) with the sun, much like Comet Shumaker-Levy (sp?) was torn apart just prior to impact with Jupiter ca. 1994.