If earths rotation stoped, the moon would be released.

[cvjacques]

A friend insist that gravity is due to Earth's rotation and that if it stopped spinning the moon would sease to orbit and would be lauched in space!

Is that right?

What pourcentage of Earth's gravity is caused by it's rotation?

I thought the gravity came from it's mass!

Thanks

Eric

 

[berkeman]

A friend insist that gravity is due to Earth's rotation and that if it stopped spinning the moon would sease to orbit and would be lauched in space!

Is that right?

What pourcentage of Earth's gravity is caused by it's rotation?

I thought the gravity came from it's mass!

Thanks

Eric

Welcome to the PF.

As you and your friend take more physics and science classes, you will learn that gravity is due to mass, and has nothing to do with the spinning of the masses on their axes:

http://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation

.

 

[cvjacques]

Thanks! I owe you have the beer I just won...lol!

 

[zhermes]

You are entirely right Eric; gravity comes from mass, not rotation.
Earth's rotation has a very very very small effect on the surface gravity (decreases it a little bit); but virtually no effect on the moon.

 

[Nik_2213]

"...virtually no effect on the moon."

Other than the tidal dissipation making Moon recede just fast enough to be measured by laser ranging...
;-))

 

[Phobos]

...and tidally locking the moon

 

[DaveC426913]

I think tidal locking of the Moon is due to the Moon's irregularity, not due to Earth's rotational irregularity.

 

[sophiecentaur]

I have a feeling that, but for a loss mechanism, like the tides, the irregularity of the Moon would just produce an undamped rotational oscillation (yawing) - not locking.
The tides, of course, are also the mechanism that is 'dragging' the Moon backwards and increasing the orbital radius at a very low rate.

[edit - owch, I meant Forwards]

 

[shashankac655]

Is the moon spending any energy by revolving around the earth? i heard that the moon is constantly losing it's angular momentum and is moving away from the Earth and one day(over millions of years) break free of Earth's gravity?

 

[DaveC426913]

Is the moon spending any energy by revolving around the earth? i heard that the moon is constantly losing it's angular momentum and is moving away from the Earth and one day(over millions of years) break free of Earth's gravity?

Yes and no.

If both Moon and Earth were solid perfect spheres, and in a neighborless Solar System, no. In this ideal circumstance no energy is expended. They would happily revolve for eternity.

But both Moon and Earth are irregular ibodies, and Earth is not totally solid (oceans). They pull on each other imperfectly. This push and pull results in a slight acceleration of the Moon in its orbit. Faster orbit means higher orbit, so the Moon starts receding. But the Moon's recession will not continue forever, it will reach an equilibrium, and will not result in it escaping Earth's orbit. That would require a catastrophic event.

So, in reality, they are transferring energy back and forth - though even at that, the Earth-Moon system is not expending any energy.

 

[EMFsmith]

Yes and no.


But both Moon and Earth are irregular ibodies, and Earth is not totally solid (oceans). They pull on each other imperfectly. This push and pull results in a slight acceleration of the Moon in its orbit. Faster orbit means higher orbit, so the Moon starts receding. But the Moon's recession will not continue forever, it will reach an equilibrium, and will not result in it escaping Earth's orbit. That would require a catastrophic event.

Is this anything like the asteroid belt in our solar system, its pulled between the sun and Jupiter and has found an equilibrium?

 

[Janus]

Is the moon spending any energy by revolving around the earth? i heard that the moon is constantly losing it's angular momentum and is moving away from the Earth and one day(over millions of years) break free of Earth's gravity?

The Moon is constantly gaining angular momentum.(As it loses orbital velocity, it gains even more in orbital radius.) The tidal coupling between the Earth and Moon is transferring angular momentum from Earth to Moon and the Earth's rotation slows in return.

The Moon won't break free of the Earth. After billions of years, the Moon and Earth would become tidally locked, and the Earth will rotate with the same period as the Moon orbits. When this happens, the mechanism that transfers angular momentum from Earth to Moon goes away and they reach a stable configuration( More or less, the Sun's tidal friction on the Earth will work against the Earth's rotation, in reaction, the Moon will start to transfer angular momentum to the Earth and will start to "reel in" towards the Earth.

More importantly, however, is the time scale involved. Before the Moon and Earth can even become tidally locked, our Sun will swell into a red giant, likely engulfing both Earth and Moon.

 

[narrator]

Yes and no... So, in reality, they are transferring energy back and forth - though even at that, the Earth-Moon system is not expending any energy.

I imagine Sol adds to that energy equation a tad.

edit: oops, I think Janus just said that

 

[nikhil khatri]

moon is bound in its orbit due to Earth's gravity .It is revolving around Earth since there is no external force to stop it ,so even Earth stops rotation moon will continue its revolution until any external force stop it .

 

[sophiecentaur]

It must be realized that the scenario of the Earth's losing rotation is not going to happen. Any event that could cause that would have to be so precise and massive that the Moon would also be hugely affected.

 

[DaveC426913]

It must be realized that the scenario of the Earth's losing rotation is not going to happen. Any event that could cause that would have to be so precise and massive that the Moon would also be hugely affected.

What?

The Earth is slowing its rotation and will eventually be tidally locked with the Moon.

 

[sophiecentaur]

What?

The Earth is slowing its rotation and will eventually be tidally locked with the Moon.

Sorry. I meant completely lost. That couldn't happen as angular momentum of the system will be conserved.

 

[EMFsmith]

A glance at Newtons's Law of Universal Gravitation will tell you that gravity is always a two-way street - just as the moon raises tides on earth, so Earth must cause tides to sweep across the surface of the moon. These tides are not in water, of course, but in the solid rock of the lunar surface. In an amazing piece of planetary heavy lifting, the moons crust would have been distorted by up to 7 meters!
This giant tidal bulge sweeping across the moon had an interesting effect. As the moon turned beneath the Earth, the rock tide was dragged across its surface, but the rising of the tides isn't instantaneous; it takes time for the surface of the moon to respond to the pull of the earth. During that time, the moon will have rotated a bit, carrying the peak of the rock tide with it. The tidal bulge will therefore not be in perfect alignment with Earth, but slightly ahead of it. Earths gravity acts in the misshapen Moon in such a way that it tries to pull it back into sync; in other words, it works like a giant brake. Over time, this effect, known as Tidal Locking, gradually synchronizes the rotation rate of the moon with its with its orbital period, effectively meaning that the tidal bulge can remain in exactly the same place on the moons surface beneath the Earth and doesn't have to be swept around.
The moon is now almost, but not quite, tidally locked to Earth, which means that it takes one month to orbit the Earth and one month to rotate around on its axis. So there's no dark side of the moon-the side we can't see gets plenty of sunlight, it's just a side that perpetually faces away from the Earth. The Earth-Moon system is in fact still evolving towards being perfectly tidally locked, and in one interesting consequence of this is that the Moon is gradually drifting further and further away from the Earth at a rate of just under 4 centimeters per year.

I hope this helps.

 

[narrator]

... and in one interesting consequence of this is that the Moon is gradually drifting further and further away from the Earth at a rate of just under 4 centimeters per year.

Though I knew this was happening, it only just now occurred to me that the drift must be accelerating, even if only at the tiniest rate.

 

[sophiecentaur]

Though I knew this was happening, it only just now occurred to me that the drift must be accelerating, even if only at the tiniest rate.

What would be the reasoning behind that assertion? Are you referring to the 1/r potential?

 

[narrator]

What would be the reasoning behind that assertion? Are you referring to the 1/r potential?

Excuse my ignorance, I may know it as something else, but what is the 1/r potential?

As for my reasoning: At some point, perhaps when the moon breaks free, it will depart from us at a much faster rate. Unless the drift remains at a constant speed until it does break free, then it must be accelerating away from us even now, if only at a tiny rate of acceleration.

 

[sophiecentaur]

Gravitational potential follows a 1/r law(?).
Why do you suggest that the Moon can "break free"? That is not what is happening at all.

 

[Ophiolite]

What?

The Earth is slowing its rotation and will eventually be tidally locked with the Moon.

I believe Sophie was referring back to the OP which implied a sudden, abrupt cessation of rotation.

 

[EMFsmith]

Though I knew this was happening, it only just now occurred to me that the drift must be accelerating, even if only at the tiniest rate.

Even though the Moon is drifting away, Gravity has an infinite range, the Moon will not just drift off into space and loose its orbit with Earth.

 

[narrator]

Gravitational potential follows a 1/r law(?).
Why do you suggest that the Moon can "break free"? That is not what is happening at all.

I read the following from a http://en.wikipedia.org/wiki/Gravitational_potential"

In classical mechanics, the gravitational potential at a location is equal to the work (energy transferred) per unit mass that is done by the force of gravity as an object moves to that location from a reference location. It is analogous to the electric potential with mass playing the role of charge. By convention, the gravitational potential is defined as zero infinitely far away from any mass. As a result it is negative elsewhere.

I think I understand it, but I could be wrong. I'm not sure I understand the "as an object moves" part. Is there a better way of wording it?

Why do I suggest the Moon can break free? If it's moving away from us at 4cm/year then at some point won't its own inertia will be stronger than the gravity which keeps it in orbit? Or will it remain in orbit, regardless of distance (at least until some other body pulls it from us)?

 

[Nik_2213]

"...though even at that, the Earth-Moon system is not expending any energy."

IIRC, the system is losing some energy to tidal friction / turbulence. The Moon's 'retreat' rate seems to have altered when the passage between South America and Antarctica opened, so tides could flow over the sill. Previously, 'retreat' rates seem to have depended on continental grouping, always changing due plate tectonics...

Uh, IMHO, the Moon should reach an equilibrium at one of Earth's 'trojan' points -- L4 / L5...

 

[narrator]

Uh, IMHO, the Moon should reach an equilibrium at one of Earth's 'trojan' points -- L4 / L5...

I gather you mean one of the Sun-Earth trojan points...?

 

[sophiecentaur]

Why do I suggest the Moon can break free? If it's moving away from us at 4cm/year then at some point won't its own inertia will be stronger than the gravity which keeps it in orbit? Or will it remain in orbit, regardless of distance (at least until some other body pulls it from us)?

It may be moving away at that rate at the moment but, as it gets further away, its Kinetic energy is getting less because the total Energy (PE plus KE plus rotational energy of the two bodies) of the system is constant (in fact, it's reducing because of energy lost as heat through friction). It is, basically, slowing down in its recession for the same reason that a ball slows down when thrown upwards. Its orbit is getting a small amount of energy from the Earth's rotation but this is only whilst it lags behind the Earth. When they become totally locked there is no more energy available to ' throw the Moon off any further.
As with many situations, you need to consider the availability of Energy if you want to determine what will happen. In this case, there would never be enough energy available for tho Moon actually to escape.

 

[narrator]

As with many situations, you need to consider the availability of Energy if you want to determine what will happen. In this case, there would never be enough energy available for tho Moon actually to escape.

Thanks for the explanation. That makes sense. I suppose I sometimes compare the gravity of celestial objects with the attraction between magnets, while forgetting the overriding force of Earth's gravity on the two magnets (amongst other differences).

 

[DaveC426913]

"...though even at that, the Earth-Moon system is not expending any energy."

IIRC, the system is losing some energy to tidal friction / turbulenceb.

No. They are trading energy back and forth, changing rotations and orbital altitudes, but the the system is not losing any energy to some external recipient.

 

[D H]

Though I knew this was happening, it only just now occurred to me that the drift must be accelerating, even if only at the tiniest rate.

In the long term, the rate is decreasing, not increasing. Tidal force is roughly a 1/r³ force. As the Moon recedes from the Earth the tidal forces on the Earth decrease (and decrease quickly thanks to that 1/r³ form). It is these tidal forces that drive the transfer of angular momentum from the Earth's rotation to the Moon's orbit.

The growing consensus is that the Moon formed at about 4 to 6 Earth radii from the center of the Earth from the remnants of a collision between the proto-Earth and a Mars-sized body. That early Moon receded rather quickly from that initial orbit thanks to the huge tidal forces at such short distances.

 

[Nik_2213]

Tidal Friction, really...

According to Wiki (YMMV)...
http://en.wikipedia.org/wiki/Tidal_acceleration

"The rotational angular momentum of the Earth decreases and consequently the length of the day increases. The net tide raised on Earth by the Moon is dragged ahead of the Moon by Earth's much faster rotation. Tidal friction is required to drag and maintain the bulge ahead of the Moon, and it dissipates the excess energy of the exchange of rotational and orbital energy between the Earth and Moon as heat. If the friction and heat dissipation were not present, the Moon's gravitational force on the tidal bulge would rapidly (within two days) bring the tide back into synchronization with the Moon, and the Moon would no longer recede. Most of the dissipation occurs in a turbulent bottom boundary layer in shallow seas such as the European shelf around the British Isles, the Patagonian shelf off Argentina, and the Bering Sea.[10]

"The dissipation of energy by tidal friction averages about 3.75 terawatts, of which 2.5 terawatts are from the principal M2 lunar component and the remainder from other components, both lunar and solar.[11]"

And... http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html

"The tidal braking in the Earth's rotation is actually caused primarily by friction in the oceans, where ``friction'' may refer to any number of physical mechanisms which have yet to be determined definitively. For example, bottom friction, induced by tidal currents flowing across the seabed, various kinds of wave breaking, and scattering of tidal waves into oceanic internal waves are all thought to play a role. For a recent overview of this subject, look up Walter Munk's paper ``Once again: once again--tidal friction,'' published in Progress in Oceanography, vol. 40, pp. 7-36, 1997."

Unfortunately, the link to that paper is broken, but Google found...
http://champs.cecs.ucf.edu/Library/Journal_Articles/pdfs/Once%20again,%20once%20again%20-%20tidal%20friction.pdf

 

[D H]

No. They are trading energy back and forth, changing rotations and orbital altitudes, but the the system is not losing any energy to some external recipient.

Sure it is.

While angular momentum is conserved here, mechanical energy is not. As mentioned in the previous post, it is the lossiness of the system that ultimately is the cause of the recession of the Moon and the slowing of the Earth's rotation rate.

 

[DaveC426913]

Sure it is.

While angular momentum is conserved here, mechanical energy is not. As mentioned in the previous post, it is the lossiness of the system that ultimately is the cause of the recession of the Moon and the slowing of the Earth's rotation rate.

All the energy of which is conserved in the Earth-Moon system.

 

[D H]

All the energy of which is conserved in the Earth-Moon system.

No, it is not.

Write the equations for angular momentum and mechanical energy. One is conserved, the other is not. The lost mechanical energy is transformed to heat, and that heat radiates away.

 

[DaveC426913]

No, it is not.

Write the equations for angular momentum and mechanical energy. One is conserved, the other is not. The lost mechanical energy is transformed to heat, and that heat radiates away.

Ah. OK. I was about to ask you how the energy escapes the system.

 

[narrator]

No, it is not.

Write the equations for angular momentum and mechanical energy. One is conserved, the other is not. The lost mechanical energy is transformed to heat, and that heat radiates away.

That's what I was wondering. If any system creates heat, it's generally energy lost to that system, unless that heat energy can be converted to something else. Heat energy must be one of the most inefficient forms, in any localized sense.

What percentage or proportion of the total energy in the Earth-Moon system would be heat energy? I imagine it would have to be tiny. Can it be computed from the displacement of the Moon's movement away from the Earth? Lay questions, so please excuse if I'm wildly off track.

 

[Nik_2213]

From my post above...

"The dissipation of energy by tidal friction averages about 3.75 terawatts, of which 2.5 terawatts are from the principal M2 lunar component and the remainder from other components, both lunar and solar.[11]"

 

[narrator]

From my post above...

"The dissipation of energy by tidal friction averages about 3.75 terawatts, of which 2.5 terawatts are from the principal M2 lunar component and the remainder from other components, both lunar and solar.[11]"

And the total energy in the Earth-Moon system is... ?

 

[ttown_okie]

If the Earth stopped spinning, then the Earth's magnetic field has also stopped. One of two things would happen. The moon would go out to a more distant orbit or it would come crashing to Earth do to the magnetic lock with Earth being affected by the lose of Earths Magnetic field.

 

[zhermes]

If the Earth stopped spinning, then the Earth's magnetic field has also stopped. One of two things would happen. The moon would go out to a more distant orbit or it would come crashing to Earth do to the magnetic lock with Earth being affected by the lose of Earths Magnetic field.

NO! Don't make things up!

 

[JaredJames]

If the Earth stopped spinning, then the Earth's magnetic field has also stopped. One of two things would happen. The moon would go out to a more distant orbit or it would come crashing to Earth do to the magnetic lock with Earth being affected by the lose of Earths Magnetic field.

This is the second thread in a row you've posted nonsense in.

I recommend you do a bit of reading before posting further because the above is complete and utter rubbish.

 

[ttown_okie]

This is the second thread in a row you've posted nonsense in.

I recommend you do a bit of reading before posting further because the above is complete and utter rubbish.

It is not rubbish, if you understood why the Earth has spin and the reason the moon is orbiting the Earth with one face always facing Earth to begin with you might then be able to better understand what would happen to the moon if the Earth were to suddenly stop which is what this topic asked.

 

[JaredJames]

It is not rubbish, if you understood why the Earth has spin and the reason the moon is orbiting the Earth with one face always facing Earth to begin with you might then be able to better understand what would happen to the moon if the Earth were to suddenly stop which is what this topic asked.

Nothing in your post has any scientific value.

Spinning or not, the Earth's gravitational attraction on the moon is the same. It is only the tidal issue that will have an effect.

Nothing to do with magnetic fields.

Bear in mind the magnetic field can barely move the needle on a compass, and its power drops off at the square of the distance. It really isn't that strong.

 

[sophiecentaur]

If the Earth stopped spinning, then the Earth's magnetic field has also stopped. One of two things would happen. The moon would go out to a more distant orbit or it would come crashing to Earth do to the magnetic lock with Earth being affected by the lose of Earths Magnetic field.

This is such nonsense. Have you no conception of conservation of angular momentum or the relative magnitudes of the fields involved? Why do you write such stuff with absolutely no basis in fact? Physics is not just a set of fairytales that someone made up, you know.

 

[ttown_okie]

Nothing in your post has any scientific value.

Spinning or not, the Earth's gravitational attraction on the moon is the same. It is only the tidal issue that will have an effect.

Nothing to do with magnetic fields.

Bear in mind the magnetic field can barely move the needle on a compass, and its power drops off at the square of the distance. It really isn't that strong.

You can not separate electricity and magnetic fields and you probably can not separate gravity from electromagnets either. In fact the a popular current theory is that north and south poles are holding together all matter itself, see quarks and string theory.

The compass aligns itself with the stream of magnetic particles flowing out of the south and north poles back around to the other pole and through the core of the Earth. When you have two highly concentrated streams of currents flowing in opposite directions along magnetic field lines you will generate a force perpendicular to the magnetic field lines and there is a rotation to it because the streams are going in opposite direction and as they pass twist around each other in a screwlike fashion. You can see this yourself by generating plasma along the outside of a wire and observing the currents twist around each other in a spin. If you understand how electricity is generated you would know this.

To say that if Earths magnetic field were to go away that it would have an impact on the moons movement is not nonsense. Stop ridiculing my posts just because you do not agree or understand. I think all of the fundamental forces are working together in this problem that the OP asked but when I bring up the electro-magnetic some of you get upset.

 

[JaredJames]

You can not separate electricity and magnetic fields

No one said you can. Moot point.

and you probably can not separate gravity from electromagnets either.

Uh, what? Are you saying that gravity on Mars is different because it has an incredicbly weak magnetic field?

In fact the a popular current theory is that north and south poles are holding together all matter itself, see quarks and string theory.

The guy who couldn't grasp reference points in the other thread is lecturing on string theory?

The compass aligns itself with the stream of magnetic particles flowing out of the south and north poles back around to the other pole and through the core of the Earth.

Magnetic particles?

When you have two highly concentrated streams of currents flowing in opposite directions along magnetic field lines you will generate a force perpendicular to the magnetic field lines and there is a rotation to it because the streams are going in opposite direction and as they pass twist around each other in a screwlike fashion. You can see this yourself by generating plasma along the outside of a wire and observing the currents twist around each other in a spin. If you understand how electricity is generated you would know this.

And this has what to do with your point?

To say that if Earths magnetic field were to go away that it would have an impact on the moons movement is not nonsense.

Have you calculated the strength of the Earths magnetic field on the moon?

Stop ridiculing my posts just because you do not agree or understand. I think all of the fundamental forces are working together in this problem that the OP asked but when I bring up the electro-magnetic some of you get upset.

What you think is irrelevant. What does the strong and weak nuclear force have to do with anything here, let alone the electromagnetic force? Science just doesn't agree with you.

Of course, you could prove everyone here wrong and start producing citations to published papers to back up what you're claiming...

 

[DaveC426913]

Stop ridiculing my posts just because you do not agree or understand.

They are not ridiculing them; they are pointing out that they are factually incorrect in many places, showing a dramatic lack of understanding of the physics involved.

Thread reported, in prep for rolling back [strike]nonsense[/strike] factual errors.

 

[ttown_okie]

They are not ridiculing them; they are pointing out that they are factually incorrect in many places, showing a dramatic lack of understanding of the physics involved.

Thread reported, in prep for rolling back [strike]nonsense[/strike] factual errors.

You claim factual error but yet offer no evidence, just ridicule. This thread is to discuss what would happen to the moon if the Earth were to stop rotating, let's stick to the topic.

 

[DaveC426913]

You claim factual error but yet offer no evidence, just ridicule. This thread is to discuss what would happen to the moon if the Earth were to stop rotating, let's stick to the topic.

Let's stick to known science.

You do not offer science, the onus is not on me (or any of us) to refute it.



Write short posts. This thread has been reported for review and cleansing of misinformation.