# Why does the Earth Spin?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by M00se1989, Nov 26, 2010.

1. ### M00se1989BannedBanned

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Faster than the moon rotates?

Is it fluid dynamics in tides? If so I think that the Earth would rotate in sync with the moon. One day would last thirty days or maybe even less.

The moon has its orbit but does it technically even rotate relative to the sun? One side is always facing it. But the moon appears and does rotate to us. The moon does not always show us the side of the mans face. If we had a telescope on the sun it would always appear to be full. If the moon did not aid the spin then its tidal forces would make the Earth slow down. Still it is not the constant force that keeps the Earth spinning in this system. Is it possible that the moon acts like a mirror to some forces that cause the earth to spin?

3. ### ULTRARealistically SurrealRegistered Senior Member

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Greetings. The Moon is in what we call a "Locked" orbit. It does not rotate in relation to the Earth, when you look up at the Moon, you always see the same "side". The Earth used to rotate much faster than it does today. Aparrantly many millions of years ago a day only lasted about 6 hours. Tidal forces due to the Sun and Moons' gravity are helping to slow the Earth down. The Earth probably began to spin as matter accreted to form the planet, but it probably got a lot of spin when it collided with Mars early in its history knocking a big chunk into space. This cooled and began orbiting Earth, becoming the moon eventually. Analysis of the Moons' rocks, meteors, comets and Martian debris indicate this event would have forced the young Earth into a sustained period of super-vulcanicity. Basically, it melted.
In space if an object is spinning, it will simply continue to spin until something stops it. Collisions and/or gravity are the prime candidates.

5. ### M00se1989BannedBanned

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True. Perhaps the Earth and Mars were once a singular superheated ball and they seperated due to the force of this moon that collided with them. The resulting forces possibly could have resulted in similar day patterns.

7. ### Boris2Valued Senior Member

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if you were on the sun you would see the moon rotate ones every 29 days.

8. ### M00se1989BannedBanned

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That does make sense Boris. So one month on Earth is one "Moonday". Be a strange coincidence if the sun were to rotate with the same pace. The moon and the sun would always have the same side facing eachother as they rotate.

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10. ### Boris2Valued Senior Member

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eeerrrr no. don't confuse rotate with orbit.

11. ### James RJust this guy, you know?Staff Member

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Tidal friction has slowed down the rotational rate of the Moon and the Earth. Since the Moon is much less massive than the Earth, the Moon has slowed down more than the Earth.

The Moon rotates once every 29 days as seen from the Sun. From the Sun, you can see all sides of the Moon over a 29 day period.

Yes it does.

Yes.

They do.

No force is necessary to keep a planet spinning.

No.

12. ### D HSome other guyValued Senior Member

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No, it isn't fluid dynamics in tides.
No, it isn't the Moon aiding the spin.
No, it is not some constant force that keeps the Earth spinning.
No, it is not possible that the moon acts like a mirror to some forces that causes the Earth to spin.

The Earth's mass and radius are respectively 81.3 and 3.66 times those of the Moon. Those two facts alone make for a huge discrepancy in the time needed for the Moon to become tidally locked to the Earth versus the Earth becoming tidally locked to the Moon: $\left(\frac{m_e}{m_m}\right)^3\left(\frac{r_e}{r_m}\right)^2$ is about 7 million. Drop this by an order of magnitude due to the fact that the Earth's k2 Love number is 12.6 times than that of the Moon and you still a big number. All other things being equal, lot more time (about 500,000 times more time) for the Moon to tidally lock the Earth than it took for the Earth to tidally lock the Moon.

All other things are not equal. The time it takes for one body to become tidally locked to another is proportion to the sixth power of the distance between the two bodies. The Moon became tidally locked shortly after the formation of the Moon when the distance between the Earth and Moon was small. The affect of the Moon on the Earth was of course also magnified by this reduced distance.

That said, the Earth's rotation rate has slowed by quite a bit since the formation of the Moon, from about a 6 hour day to our current 24 hour day.

13. ### AlexGLike nailing Jello to a treeValued Senior Member

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Money makes the world go round, and this is the effect of inflation.

14. ### M00se1989BannedBanned

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I don't think I did... The moon takes thirty days for an orbit which to it is a rotation. Its orbit period and its rotation period are the same. And the sun rotates every 27 days (31 at the poles)http://curious.astro.cornell.edu/question.php?number=615

I am only saying that some electromagnetic forces could potentially play a role in the spin of inertial bodies in our solar system. Most planets with satellites rotate faster than those without.

15. ### BlindmanValued Senior Member

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Because the moon has a slight eccentricity to its orbit it does appear to rotate or wobble back and forth. At apogee the moon has slowed but because the moons rotation is constant it will rotate slightly to the west from our view on the earth. At perigee it is traveling faster and it will appear to rotate slightly to the east from our perspective..

We see slightly more then half of the moons face.

Moons sidereal orbit and rotation is 27.3days.

The sun at the equator rotates every 24.47 days and at the poles every 36 days. This is called the sidereal rotation period. If you take in account that the Earth is moving around the sun then your numbers are close relative to our view from Earth and is called the synodic rotation period of 26.24 days.

16. ### D HSome other guyValued Senior Member

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No, it can't.

There are only two without, Mercury and Venus. That these two planets rotate at a slower rate than the others has little if anything to do with the fact they don't have moons.

What makes the Earth keep rotating about its axis is the simple fact that it is rotating about its axis now. A force (or more precisely, a torque) is not needed to maintain that rotation. A torque is needed to change the Earth's angular momentum.

17. ### M00se1989BannedBanned

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I don't know I've been playing tennis for a long time and I think the rotation does odd things to an objects trajectory. Topspin makes balls dive, backspin make it lift. And the sidespin from the deuce court I can put on a serve to the outside corner really makes it jump away from a person in a strange way. The moon "rolls" with the sun and I think it would make a decent addition to string theory if we could understand more to why things rotate. Like how some electrons might rotate with the spin of the nucleus and have bearings on the spin of the atom itself. Wait here it is. http://en.wikipedia.org/wiki/Solar_dynamo a Solar Dynamo. Like a toroidal river in the tachocline that interplays with the mass of the whole solid structure and the gravitational forces of other bodies.

18. ### AlexGLike nailing Jello to a treeValued Senior Member

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That's because of air resistance.

19. ### Alan McDougallAlan McDougallRegistered Senior Member

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The earth spins because it was hit side on by a colossal planet, thought to be the size of Mars

At the moment of the Big Bang the so called tiny signularity was actually the largest object in existence?

20. ### D HSome other guyValued Senior Member

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Just because you do not understand why things rotate does not mean nobody understands it. Angular momentum is a conserved quantity. That means that an external torque is required to change some object's angular momentum. No torque = no change in angular momentum. A rotating body that never has a non-zero net torque acting on it will continue rotating forever with no change in angular momentum.

The Moon only rotates with the Sun if you look at things cross-eyed, and even then it is a mere coincidence. The Moon's rotation rate has varied considerably since the Moon first formed and now, and will continue varying into the future. The rotation rates coincidentally happen to be the about same at this point in time. To bring it beyond the realm of mere coincidence you need cause and effect.

Nope. That isn't it.

Nope. That isn't it either.

Last edited: Nov 27, 2010
21. ### M00se1989BannedBanned

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Space is an air that man can't breathe.

And If i had a time machine to show that the moon was a hot spinning object that came from the Sun and split Earth and Mars appart when they were still molten lava I would. We still know that at some point in time the earth mars and moon were closer to eachother than they are today and a good bit warmer.

22. ### AlexGLike nailing Jello to a treeValued Senior Member

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This might be the single most stupidest thing you've ever posted.

23. ### M00se1989BannedBanned

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You of all people should know that is a highly debatable topic you have stumbled onto. Just because your air is moving at near light speed does not mean it isn't air. Nor does it mean it becomes air when it interacts whith the Earths magnetosphere. Nor does that mean that the magnetosphere would react back to the charged particles.