I heard this on Prof. Neil Tyson's StarTalk podcast (this episode) and had a question about it. In a Q&A session, a listener had asked what would happen if Superman really did stop the earth from rotating and rotated it in the other direction. Prof. Tyson's response was that if the earth, which is rotating at approx. 1000mph about its axis, is stopped, everything that is not anchored on earth will move the opposite direction at 1000mph and we'd all go crashing into things at that speed.

I suppose that is just simple inertia: if a body moving at 1000mph is stopped abruptly, everything that was moving with it but not attached to it would indeed attempt to continue in the same direction at 1000mph. However, the earth is rotating rather than moving in a straight line. Essentially, gravity is strong enough to ensure that we are not thrown off into space by the centrifugal force from the earth's rotation (we aren't holding on to our dear lives as the earth turns at 1000mph). So in a sense, aren't we anchored to earth by gravity? And therefore, doesn't it mean that if the earth stopped abruptly, we'd just stop with it? (I'm thinking of say a centrifuge with test tubes attached to it. Though as I think about this, I feel that we'd sway at the point of attachment instead of stand still, were the earth to stop).

Can someone help resolve this for me?

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    $\begingroup$ You cannot stop earth rotating just like that. If you consider non-scientific non-sense (superman), then you shouldn't ask for a scientifically based answer either. $\endgroup$
    – Walter
    Feb 9 '14 at 18:04
  • $\begingroup$ Anything that would stop the Earth's rotation would melt it to a consistency similar to Hawaiian lava, boil the oceans, and eradicate life of every type. When you imagine that CGI version of stopping the planet's rotation, add in those details. $\endgroup$
    – Marc
    Feb 9 '14 at 19:47
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    $\begingroup$ @Walter: Sure this is "non-scientific nonsense", though Dr. Tyson thought it worthy enough of a response. I suppose my question applies to any rotating sphere with proportionally sized objects on it held by gravitational forces. $\endgroup$ Feb 10 '14 at 6:22
  • $\begingroup$ See also physics.stackexchange.com/questions/48287/… and physics.stackexchange.com/questions/137191/… $\endgroup$
    – user21
    Dec 30 '14 at 12:48
  • $\begingroup$ The explanation of NDGT is correct. Everything will continue its motion with speed as in the answer below. Flying or sliding is just because we have big feet and we cannot consider ourseelf as point mass on a circumference but rather we are object on a plane. Better sliding of course. As otherwise you have to stop abruptly by the feet. That answer should have indeed answered your question. $\endgroup$
    – Alchimista
    Jan 17 '19 at 8:50

You would be sliding, because the friction between you and Earth would be too weak, or else you wouldn't survive the acceleration, if the rotation of Earth would be changed abruptly. That's like crashing into a wall with several hundred mph. This is with the exception of close to the poles.

Your weight wouldn't change much. On a smooth, plane, and horizontal surface you would slide (due to your inertia). Your velocity you would be sliding depends on your geographic latitude. At the equator it would be at the maximum. At the poles it would be zero. More precisely the velocity would be proportional to the cosine of the latitude (latitude 0 at the equator, and (+/-) 90 degrees, resp. $\pi/2$ at the poles).

Even more precisely, the speed you would be sliding would be $$2\cdot 465.1~ m/s \cdot cos ~\varphi,$$ with $\varphi$ the latitude. Factor two, because superman accelerates to the opposite direction. Earth's equatorial rotation velocity is $465.1~m/s$.

  • $\begingroup$ Understand the explanation in isolation, but I can't say I see how this answers my specific (and admittedly somewhat vague) question. $\endgroup$ Feb 10 '14 at 6:21
  • $\begingroup$ Without sliding or additional help of superman magically annihilating your inertia you wouldn't survive this experiment. Never try it. $\endgroup$
    – Gerald
    Feb 10 '14 at 11:41

Depends on how the angular momentum (that manifests itself as Earth's rotation) would be absorbed. If, magically, it's absorbed smoothly and evenly, then not much dramatic happens initially (a small change in your weight and some earthquakes as response to the missing centrifugal forces), but the Earth climate and weather would change dramatically within about 100 hours (mind you that the day==year), the day side heating and drying up and the night side freezing.

If, on the other hand, the angular momentum is absorbed only at certain points, for example if some cosmic giant stops rotation with its finger, then all other structures would need to decelerate from the rotation, likely destroying most human constructions, causing massive flooding of the continents, crumbling of mountains, huge earthquakes, instant death to most non-microbic life forms.

  • $\begingroup$ When you say "If magically, it's absorbed smoothly and evenly", are you referring to a hypothetical situation where the earth just stops rotating abruptly? $\endgroup$ Feb 10 '14 at 6:19

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