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Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events?

John
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  • Not a real question... – Sklivvz Apr 03 '11 at 14:35
  • I couldn't make heads or tails about this "question"!! –  Apr 03 '11 at 15:55
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    -1 When using the word 'given' in a physics question, that which you are giving should have some obvious interpretation. 'No conflicting events' is very vague. Can you be more specific? – Nic Apr 03 '11 at 16:07
  • This question, surmising a fact contradictional to reality, should not be answered before asking, where this opinion is derived from, and what is meant by "rotation". As srange as the "question" is, I suspect that this rotation is not the rotation around the earths axis. Always assume maximal absurdity. :=( – Georg Apr 03 '11 at 20:08

5 Answers5

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The question in ill-stated and open to multiple interpretations. I'm going to answer two of them.

  1. Assuming that by planet you mean a more-or-less solid object (like the Earth), then no. Conservation of angular momentum means that unless acted on by a non-central outside force the speed of rotation remains forever the same.

  2. Assuming that the planet is an warm, gaseous object (like Jupiter shortly after the formation of the solar system), than the system is supported in part by Virial heating, and will continue to contract as it cools. Because Angular momentum is conserved in this system too, as the body contracts it's speed of rotation will increase. Eventually however, the contraction will stop as processes other than thermal pressure in the gas begin to dominate. Once that happens we're back to the first case: the rate of rotation is fixed.

dmckee --- ex-moderator kitten
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A planet with no forces acting on it will rotate at the same speed for ever.

However a real planet will experience tidal forces which will eventually slow it's rotation until the same side always faces the sun (or possibly until it reaches a resonance with the sun's influence and other nearby large planets)

Martin Beckett
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No, it will continue to rotate at the same rate forever. This is a consequence of angular momentum conservation.

http://en.wikipedia.org/wiki/Angular_momentum

TROLLHUNTER
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Your question does lack a few specifics, but it's not at all incomprehensible? Common sense indicates that your initial premise must come from a basic example taught in public schools. That is that if you launch a rocket or spacecraft into outer space, it will continue to accelerate faster and faster. But unlike an orbiting planet which is defined by conservation of angular momentum, a rocket has a propulsion system with certain differing variables in each application. Although the immediate answer is no. I would recommend rephrasing your question after reviewing angular moment

tigerskill
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The answer is 'No'. If you have to answer at school then the previous answers are fine, consistent whith mainstream.

But ...
The answer is 'Yes' under this undiscussed model (page 11, Rotation, eq 38) where the variation of LOD (Earth's Length Of Day) is discussed. A less known fact is that the Earth is increasing the long term rate of rotation, i.e. shorter days (image from here). The angular momentum redistribution due to tidal effects is not enough to account for the measures, because it implies a slowing instead of an acceleration of rotation. The overall redistribuition of water/ice and movement of the solid crust is also not sufficient to account for the measures.

My personal answer is 'Yes' because I can not find a single reason to disproof that model .
The extreme rotational speed of millisecond pulsars can be easily explained by model, as suggested there.
$\Delta$LOD - Length Of Day

Helder Velez
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    -1 This plot is very misleading, because it starts at 1973, which was a local maximum of the day length. If you go back to 1960, the day length is pretty much the same now as it was then. I believe geopaleontological studies have shown that the earth's day is quite a bit longer now than it was billions of years ago, but for century time-scales this change is so small it's drowned out by random fluctuations. Here is the real plot. – Peter Shor Apr 04 '11 at 14:49
  • Satelite data, since 1973, are the most accurate ever made. At your graph the green line : 'Moving 365-day average of deviation' is the important one. One must not be misleaded by 'leap-seconds' because these are not measures. In that paper the ref[27] concludes: palaeoclimate record from the eastern Mediterranean Sea over the past three million years is 1.1 ms c$y^{-1}$. – Helder Velez Apr 04 '11 at 15:15
  • 3 down votes ... But everyone 'knew' that the earth was slowing down the rotation. This earth is so inconvenient and that graph is horrendous. Thumbs down because everyone knows that that model is rubbish and after all nobody likes to be defied nor defeated by new ideas. Anyway that model can only account for 10% of the acceleration. – Helder Velez Apr 05 '11 at 14:43
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    If you're going to ignore exactly those 11 years of data that make your theory look best, waving your hands and saying "satellite data are more accurate" is not adequate justification. Are the error bars on the pre-1973 data really big enough to justify this? It certainly doesn't look so from the graph. And further, the paper ref[27] really does show the day is getting longer, just not as fast as the current models predict it should. From the graph, you can see that the 1.1 ms/century rate given in that paper would be completely drowned out by the random fluctuations over the last 40 years – Peter Shor Apr 06 '11 at 00:11
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    For contrary evidence see Williams, George E. (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics 38 (1): 37–60. Bibcode 2000RvGeo..38...37W. doi:10.1029/1999RG900016 – dmckee --- ex-moderator kitten Apr 30 '11 at 16:17