Fact: The Earth is rotating on it's own axis every 24 hours.

Question: If, for some reason I won't specify the current speed of the Earth and could slow it down(say by 5%). Will it speed up again back to its previous speed of its own?

Let's suppose the Earth's speed is decreased by 50%. Such that its period of rotation will be 48 hours. Would its period gradually return to 24 hours?


closed as unclear what you're asking by Kyle Oman, John Rennie, yuggib, RedGrittyBrick, rob Jun 1 '15 at 22:27

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  • $\begingroup$ I'm not sure what you're asking, specifically what you mean by "normal"? $\endgroup$ – Kyle Oman Jun 1 '15 at 16:08
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    $\begingroup$ Are you asking, "if the Earth was slowed down, would it naturally speed back up"? $\endgroup$ – zeldredge Jun 1 '15 at 16:08
  • $\begingroup$ I suppose what your asking is why 24 hours? Is 24 hours some kind of natural time-scale for the Earth's rotation, that it would return to if perturbed $\endgroup$ – innisfree Jun 1 '15 at 16:24
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    $\begingroup$ I find this question pretty clear, though somewhat strange. $\endgroup$ – Walter Jun 2 '15 at 17:22
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    $\begingroup$ what leads you to believe that Mars has a solid-liquid core? The preliminary searching I did indicates that we aren't sure if Mars has a solid or a liquid core $\endgroup$ – Jim Jun 4 '15 at 17:35

If we consider the earth as an isolated system there are no reasons to have our planet to change its angular momentum, due to conservation of the latter.

However if we consider the earth and its neighbourhood we have that the earth is actually decelerating because of the Moon. The Moon has an orbital period longer then the rotational period of the earth, from this the Moon is subject to tidal acceleration. Since the Moon is accelerating, i.e. is gaining rotational energy, the earth will decelerate since this energy is drained out from the angular momentum of the earth.

The only way our earth can gain angular momentum, as any other body, is by external forces (e.g. a gigantic asteroid hitting the earth).

  • $\begingroup$ I don't agree. Because, Mercury and Venus were never got hit by any gigantic bodies & Earth & Mars are on close to same speed, that means they were hit by more or less common force & also that would be same for Jupiter & Saturn as well? Uranus & Venus as well? I think the speed of rotation of earth is decided by the change of inner magnetic force? What i think the Earth is nothing but a Torque Motor. $\endgroup$ – Debasis Chakrabarty Jun 1 '15 at 16:42
  • $\begingroup$ There are many geological and biological proofs that the rotation got slower regularly. Is the motor faltering ? If an internal engine provides a continuous rotating force without friction counterparts, the equatorial Earth surface speed might reach c quickly . $\endgroup$ – user46925 Jun 1 '15 at 17:07
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    $\begingroup$ Note that Snaporaz is careful to talk about the angular momentum being constant. The usual ice-skater example shows how angular velocity can change while angular momentum stays constant. You could imagine some Science Fictional scenario in which the crust is lifted on a miles high scaffold (for some unspecified reason) causing a slowing of rotation that then resumes again after civilization falls and the scaffold crumbles. Indeed earthquakes can cause small but measurable changes in the length of the sidereal day. $\endgroup$ – dmckee Jun 1 '15 at 17:35
  • $\begingroup$ @dmckee agreed with you. Mercury & Venus have a solid core and no liquid inside, so it revolves very slowly. But Earth & Mars have a solid inner core with a liquid(or semi liquid), so they are revolving 24 hours & 24.7 hours respectively, due to distance from sun, similarly jupiter & saturn have same construction inside but they revolving with 10.0 & 10.45 hours respectively, Uranus and Neptune revolving with 17 & 16 hours respectively, and both of them have a different distance. Actually what i think is, the reaction due to heat takes place inside the core, that affects the speed of a planet $\endgroup$ – Debasis Chakrabarty Jun 3 '15 at 16:36
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    $\begingroup$ @DebasisChakrabarty This is not a medium for pushing unpublished personal theories. We can tell you what accepted mainstream physics says about the matter, but we will not discuss the potential of any of your ideas. If you do not agree with mainstream physics, that is your prerogative, but this isn't the place to argue against it. $\endgroup$ – Jim Jun 8 '15 at 15:28

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