QUESTION: Can a planet speed up it's rotation independent from external force?

This is the purpose of this thread. I'm curious if it is possible for a planet to speed up it's spinning upon it's axis without external influences (such as being struck by an object).

Can a planet speed up it's rotation independent from external force?
(without any "mega-volcano" acting like a source of propulsion)


I thank you in advance for your contributions.

Sure, the Sumatra earthquake that caused the tsunami caused the rotation to speed up, but only buy a few microseconds.

According to US scientists, the deadly earthquake was forceful enough to accelerate the Earth's rotation, and may have made the planet wobble on its axis.

Richard Gross, a geophysicist with the US space agency's Jet Propulsion Laboratory in California, believes a shift of mass toward the Earth's centre during the quake caused the planet to spin three microseconds faster and tilt about 2.5cm (one inch) on its axis.

news.bbc.co.uk...

It is the conservation of angular momentum, just like an ice skater spinning can speed up and slow down by moving their arms in and out. Earthquakes can change the shape of the surface of the planet and cause the rotation to speed up or slow down.

Originally posted by Hal9000
Sure, the Sumatra earthquake that caused the tsunami caused the rotation to speed up, but only buy a few microseconds.

Thanks Hal9000. This is actually what caused me to ask the question.

It is the conservation of angular momentum, just like an ice skater spinning can speed up and slow down by moving their arms in and out. Earthquakes can change the shape of the surface of the planet and cause the rotation to speed up or slow down.

I read/heard that the shape of the planet had changed, but was not aware of exactly how much, and over how much of the entire planet was affected. i didn't think about the skaters, but thought about "marry go-rounds" when i was a child, and sort of thought it might be a similiar effect. But i was curious about how an entire planet could excell it's rotation independant of external cause.

Your answer does make sense, and thanks for the time you spent giving me a thoughtfull answer.

Thanks,
john

That's correct, you can change the spin as long as the angular momentum is conserved.

As far as an 'external force', this may be somewhat strange, but given that electromagnetic fields and hence waves carry momentum, you can even change the angular momentum of an object by emitting or absorbing EM radiation or interacting with EM fields.

So in this case you can even change the angular momentum without a "mechanical" type of interaction. But the global conservation of momentum is still upheld.

the second law of thermodynamics states(paraphrased): the Inevitable and steady deterioration of a system.

so by natural means the planet itself will slow down as the internal temperature lowers. now this doesnt quite answer your question but does lend a point, that without an external or other anomalous event occurring an increase in speed will not occur.

the second law of thermodynamics states(paraphrased): the Inevitable and steady deterioration of a system.

so by natural means the planet itself will slow down as the internal temperature lowers.

The second law of thermodynamics was not correctly paraphrased, and does not predict any such effect. The 2nd law of thermodynamics doesn't allow violation of conservation laws like angular momentum.

The notion of a "steady deterioration" makes no sense scientifically either, it is far too vague.

The cause of the 2nd law of thermodynamics is the underlying chaotic dynamics of molecules and atoms when they come in contact.

i paraphrashed it, but the second law is focused on entropy. and steady deterioration is not that vague it simple means through a measure of #time a state of breakdown occurs

im sure you know this but atoms do not stay atoms for all eternity, they breakdown difussing into particles, then diffuse futher into pure space.

this notion of effect is defined under the 2nd law of thermodynamics.

all things decay, the duration of decay is determined by the stability of the particles. once a particle is made under fusion it begins its journey toward dissipation.

conservation of angular momentum can be obtained in a system of stable gravity or stable centrifical force this is ture, however this stablity does not stay as is for all time, it breaks down. which in turn undermines conservation.

a supernova is a large example of the 2nd law occuring- all stars die as do all particles die.

your EM waves are theorised to be the effect of matter decay.

[edit on 19-12-2006 by Glyph_D]