Does Moon revolves itself ?

[pravin.sonar]

Does Moon revolves around itself ?

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Does Moon revolves around itself ?

[swansont]

If the moon did not revolve, it would always face a fixed point in space. Does it do this?

[Akhenaten2]

swansont

I'm afraid I have to strongly disagree with your answer. Relativity theory as you know it, requires bodies to follow a straight line in curved space. The moon follows its curved orbit completely around the Earth at all times gravitationally locked into the same attitude relative to the Earth. If you straighten out that orbit the moon will not rotate about its own axis. It actually rotates only about the centre of rotation for the Earth/Moon system. This moon rotation is a long-standing error of physics and should be taught correctly.

[Sisyphus]

swansont

I'm afraid I have to strongly disagree with your answer. Relativity theory as you know it, requires bodies to follow a straight line in curved space.

 

Really? So when I walk around a corner, I'm really going in a straight line through space that is bent 90 degrees?

[tomgwyther]

Really? So when I walk around a corner, I'm really going in a straight line through space that is bent 90 degrees?

 

yes, if you're next to a massive object. e.g if you walked from the north pole to the equator.

[swansont]

swansont

I'm afraid I have to strongly disagree with your answer. Relativity theory as you know it, requires bodies to follow a straight line in curved space. The moon follows its curved orbit completely around the Earth at all times gravitationally locked into the same attitude relative to the Earth. If you straighten out that orbit the moon will not rotate about its own axis. It actually rotates only about the centre of rotation for the Earth/Moon system. This moon rotation is a long-standing error of physics and should be taught correctly.

 

Moon orbit and moon rotation are separate motions, and one need not invoke relativity to answer the question.

[MaxHenger]

I assume tomgwyther is talking about a motion of an object that is (almost entirely) uninfluenced by any other force. For example, a moon that is spinning around an heavy object, like the earth.

[tomgwyther]

I assume tomgwyther is talking about a motion of an object that is (almost entirely) uninfluenced by any other force. For example, a moon that is spinning around an heavy object, like the earth.

 

Pretty much, just a thought experiment about walking around - an albeit large - 90 degrees turn.

[Moontanman]

The moon rotates once on it's own axis every orbit of the earth, this results in the moon always showing one face to the earth. If the moon did not rotate you could see it's entire surface each time it orbited the Earth.

 

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

 

The Moon is in synchronous rotation, which means it rotates about its axis in about the same time it takes to orbit the Earth. This results in it nearly always keeping the same face turned towards the Earth. The Moon used to rotate at a faster rate, but early in its history, its rotation slowed and became locked in this orientation as a result of frictional effects associated with tidal deformations caused by the Earth.[13]

Edited February 17, 2010 by Moontanman

[Neil9327]

swansont

I'm afraid I have to strongly disagree with your answer. Relativity theory as you know it, requires bodies to follow a straight line in curved space. The moon follows its curved orbit completely around the Earth at all times gravitationally locked into the same attitude relative to the Earth. If you straighten out that orbit the moon will not rotate about its own axis. It actually rotates only about the centre of rotation for the Earth/Moon system. This moon rotation is a long-standing error of physics and should be taught correctly.

 

Interesting.

 

This raises a question: Discounting the moon's gravity, is there any centrifugal force experienced by someone on the moon's surface by virtue of the rotation of the moon?

[Sisyphus]

yes, if you're next to a massive object. e.g if you walked from the north pole to the equator.

 

This is incorrect. That's not a straight line. I think there's some confusion here, I'm guessing based on the fact that light always travels in a straight line, i.e. follows the curvature of space exactly. Walking around on the surface of the Earth or two massive bodies orbiting one another are not examples of straight lines in any sense. The moon is continually accelerated at right angles to its velocity.

[Pangloss]

Oh no. It's an airplane-on-a-treadmill question. Run for your lives!

[tomgwyther]

This is incorrect. That's not a straight line. I think there's some confusion here, I'm guessing based on the fact that light always travels in a straight line, i.e. follows the curvature of space exactly. Walking around on the surface of the Earth or two massive bodies orbiting one another are not examples of straight lines in any sense. The moon is continually accelerated at right angles to its velocity.

 

Oops. your absolutely right Sisyphus, I suspected I'd made a mistake soon after I wrote it. i have forthwith slapped my wrist.

[mulreay]

The moon rotates once on it's own axis every orbit of the earth, this results in the moon always showing one face to the earth. If the moon did not rotate you could see it's entire surface each time it orbited the Earth.

 

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

 

Just the fact you used Wiki is detrimental to your course.

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Wiki should be laughed at and shunned on every corner.

[Cap'n Refsmmat]

Or, better yet, improved.

[mulreay]

Or, better yet, improved.

 

Agreed but by who? The people that already post wiki 'facts'.

[swansont]

Just the fact you used Wiki is detrimental to your course.

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Wiki should be laughed at and shunned on every corner.

 

Argument from anti-authority is weak.

[Akhenaten2]

Moontanman

I wrote a full answer but lost it all before I could post so I'll just say yes is seems that way to us but unless GR is wrong it says we must view the orbit as a straight line in curved Space - in which case it does not rotate about its own axis other than a tiny residual oscillation from capture and reciprocal tidal effects.

[Moontanman]

Moontanman

I wrote a full answer but lost it all before I could post so I'll just say yes is seems that way to us but unless GR is wrong it says we must view the orbit as a straight line in curved Space - in which case it does not rotate about its own axis other than a tiny residual oscillation from capture and reciprocal tidal effects.

 

I see your point but it seems to me if the moon were to "loose" the bonds of earths gravity it would continue to rotate every 27.3 days.

[Akhenaten2]

Moontanman

agree with second point -the almost spherical shape of the moon points to considerable rotation at that early molten stage. The capture of its rotation would have been some sight I guess and some vestige of that rotations arrest is still present as a tiny oscillation about its axis - continuing but fuelled now by interchange of tidal effects as you describe.

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If this were possible, surely if it were suddenly freed from the earths' gravity (lets say exactly at full moon) it would simply continue parallel to the earth and its orbit, but 240k miles further out from the sun. It could not now change its orientation relative to the Earth as it is no longer "accelerated" or "pulled" from its current attitude in any way. It would of course pull ahead rapidly from the earth and soon go into an elongated elliptical orbit of its own around the sun.

Edited February 19, 2010 by Akhenaten2
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[Sisyphus]

Moontanman

I wrote a full answer but lost it all before I could post so I'll just say yes is seems that way to us but unless GR is wrong it says we must view the orbit as a straight line in curved Space - in which case it does not rotate about its own axis other than a tiny residual oscillation from capture and reciprocal tidal effects.

 

That is not what GR says. Light follows a straight line. Orbits do not. If it were a straight line, then a laser beam shined off the surface of the moon would circle around the Earth and come back again.

 

Moontanman

agree with second point -the almost spherical shape of the moon points to considerable rotation at that early molten stage. The capture of its rotation would have been some sight I guess and some vestige of that rotations arrest is still present as a tiny oscillation about its axis - continuing but fuelled now by interchange of tidal effects as you describe.

 

The spherical shape of the moon is not the result of rotation. It is a result of its own gravity pulling it into that shape, as with any other massive body of sufficient size.

[Akhenaten2]

Swansont - sorry can only post in short responses,

Moon orbit and spin are not separate but 2 effects of gravity which everyone agrees is best described by GR. You can't just switch it off because it doesn't suit your argument. I gave the standard description of how GR views the orbit of a satellite and I am happy it is correct and applicable to this query. Do you consider that GR is not representative anymore?

Akhenaten

[swansont]

Swansont - sorry can only post in short responses,

Moon orbit and spin are not separate but 2 effects of gravity which everyone agrees is best described by GR. You can't just switch it off because it doesn't suit your argument. I gave the standard description of how GR views the orbit of a satellite and I am happy it is correct and applicable to this query. Do you consider that GR is not representative anymore?

Akhenaten

 

My position is this: when someone asks a question, at a level that indicates they are a physics neophyte, I'm not going to answer the question by invoking relativity unless it's absolutely necessary. They are only going to be be familiar with Newtonian dynamics, at best, and a Cartesian geometry. It's not a matter of what is the best description of gravity, it's a matter of what is the best way to answer the question, appropriate to the knowledge level of the one asking the question.

 

One of the reasons people turn away from science is that they feel it is not accessible. I think that being given answers that are way too complicated for them is a contributing factor.

[Akhenaten2]

A neophyte being someone who doesn't agree with you? Or dares to question accepted dogma?. You choose to defend yourself rather than answer the question? OK in Newtonian Physics a force GMe.Mm/r2 acts between centres and this might make it plainer. The moon is locked gravitationally so the situation is like a hammer thrower. The weight (moon) pulled round by the athlete (earth) applying the force via a wire. The weight is restrained from rotating about its own axis - but it clearly rotates about the athlete. Same situation!

2nd point - But telling them wrong info doesn't?

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answers meant for Sisyphus:-

point 1 - I'm afraid it does.

point 2 - Yes, but not without high plasticity and rotation. Large accretion (without it building-in a rotation) is impossible in this universe. The early moon was much closer to the earth and if captured while still plastic (mostly molten) it would exhibit a much larger tidal bulge than it does.

Edited February 20, 2010 by Akhenaten2
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[swansont]

A neophyte being someone who doesn't agree with you?

 

No, when I wrote neophyte, I meant neophyte in accordance with the dictionary definition.

 

neophyte - any new participant in some activity