If earths rotation stoped, the moon would be released.

In summary: 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
  • #36
D H said:
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.
 
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  • #37
D H said:
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.
 
  • #38
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]"
 
  • #39
Nik_2213 said:
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... ?
 
  • #40
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.
 
  • #41
ttown_okie said:
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!
 
  • #42
ttown_okie said:
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.
 
  • #43
JaredJames said:
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.
 
  • #44
ttown_okie said:
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.
 
  • #45
ttown_okie said:
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.
 
  • #46
JaredJames said:
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.
 
  • #47
ttown_okie said:
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...
 
  • #48
ttown_okie said:
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.
 
  • #49
DaveC426913 said:
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.
 
  • #50
ttown_okie said:
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.
 
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  • #51
ttown_okie said:
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.

Your claims are supported by no evidence - you need to provide it. It is not up to us to disprove you. It is down to the claimant to support their statements with evidence.
 
  • #52
ttown_okie said:
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.

ttown okie, this is a science forum, and the people who have responded to you, who have attempted to correct you, are well versed in these topics (not laymen). Rather than complain, you would do better to learn from them. Even as a layman myself, I can see where you are mistaken. There is nothing wrong with mistakes, as long as you allow yourself to be corrected.

Back to my question in post #39, if the dissipation of energy by tidal friction averages about 3.75 terawatts, what's the total energy in the Earth Moon system?
 
  • #53
narrator said:
Back to my question in post #39, if the dissipation of energy by tidal friction averages about 3.75 terawatts, what's the total energy in the Earth Moon system?

I doubt total energy can be calculated from this data. I would start from known masses, radii, distance and speeds. Simple high school physics.

The only problem is - I am not sure what to include, as it depends on the definition of "total". Does the motion around Sun counts, or not?
 
  • #54
I think the Energy to go for would just be the energy that could be transferred by the inter-planetary effects. If the Solar orbit of the c.m. of the Moon-Earth didn't change then the energy of the orbit round the Sun wouldn't be relevant in this respect. You could see what a small change in this orbit would represent in the form of 'extra' energy but any tidal locking of the Moon-earth to the Sun would probably be very small, considering the geometry. Suck it and see?
 
  • #55
Interesting problem. And back to what I asked earlier, about proportion. "What percentage or proportion of the total energy in the Earth-Moon system would be heat energy?"

This is purely a guess, so please excuse. Given the masses of Earth and Moon, and excluding other influences (Sun et al) I'm thinking that the total energy between the two would be some hundreds times more than that given over to friction.

Having been a mechanical engineer in my distant past, I'm looking at it as being something like the efficiency of two well oiled gears or cogs, with one difference being that gravity is like energy normally delivered through the shaft (which I guess is where the analogy breaks down), but in engineering terms, I would expect something like 98% efficiency. And with celestial bodies suffering no physical friction or atmospheric friction, I would expect something like 99.99% efficiency.

Am I looking at this right?
 
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  • #56
narrator said:
Interesting problem. And back to what I asked earlier, about proportion. "What percentage or proportion of the total energy in the Earth-Moon system would be heat energy?"

This is purely a guess, so please excuse. Given the masses of Earth and Moon, and excluding other influences (Sun et al) I'm thinking that the total energy between the two would be some hundreds times more than that given over to friction.

Having been a mechanical engineer in my distant past, I'm looking at it as being something like the efficiency of two well oiled gears or cogs, with one difference being that gravity is like energy normally delivered through the shaft (which I guess is where the analogy breaks down), but in engineering terms, I would expect something like 98% efficiency. And with celestial bodies suffering no physical friction or atmospheric friction, I would expect something like 99.99% efficiency.

Am I looking at this right?

It's pretty easy to figure out. The moon is receding by 3.8 cm per year.

It's orbital energy is found by:

[tex]E = -\frac{G M_{earth}M_{moon}}{2a}[/tex]

with 'a' being the average Earth-Moon distance.

In the process, it lengthens the Earth's rotation period by 1.5 milliseconds/century.

The Rotational energy of the Earth is found by:

[tex]E= \frac{r^2 \omega^2M}{5}[/tex]

Where r, [itex]\omega[/itex] and M are the radius, angular velocity( in rads/sec) and mass of the Earth.

So, find the energy gained by the Moon when it climbs 3.8 meters further out and compare it to the amount of rotational energy the Earth loses by lengthening its rotation by 1.5 ms.

Compare the two and you have your answer. (you might be surprised.)
 
  • #57
So , the earth-moon system is constantly losing it's energy in the form of heat energy.Will the system lose energy like this even after the tidal locking??...if yes that means the system will continuously lose energy, but for how long? it can't lose energy forever right? ,the system must come to an end some way,how?? (just assume that the sun is not going to be a red giant and interfere with the system)
 
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  • #58
Your friend is correct. We do not know if mass creates gravity. As you are aware many things can make you experience a different gravity constant than mass itself such as changes in velocity, centrifugal force, magnetics, etc. Current physics does not understand what actually commutes gravity between points but we can observe that mass is proportional to gravity in some cases but since even this mass of planetary objects is "proven" by it's gravitational effects, one should be careful in accepting this circular reasoning.
 
  • #59
ttmark said:
As you are aware many things can make you experience a different gravity constant than mass itself such as changes in velocity, centrifugal force, magnetics, etc.

Don't confuse feeling a different force to changing gravity. There is a big difference between simulated gravity (accelerating at 1g in a spaceship) and real gravity (standing on Earth).

Whilst accelerating upwards, you experience a greater downwards force than gravity alone, but gravity itself is constant. The only way to alter the force of gravity on you is to increase either your own, or the objects mass.

There is no circular reasoning, it is observe and report. Your misunderstanding is not an excuse to attack scientific theory.

I'll leave the rest of your post to someone with more subject knowledge than myself.
 
  • #60
There is no attack here. A person on the moon certainly experiences different gravity than a person on Earth, or on any other planetary object. The effect of gravity is the summation of all the forces acting towards the systems center of mass. To describe a gravity constant you must pick a frame of reference somewhere, this is typically done at the center of mass of the system in question. To an object at rest within this system it is accepted to call that force a gravity constant and it is measured by the acceleration of that body if in free fall in a vacuum. We are able to measure a gravity constant for objects near Earth but Physics does not know what caused the gravity effect to begin with.
 
  • #61
ttmark said:
A person on the moon certainly experiences different gravity than a person on Earth,

A person on the Moon experiences gravity exactly the same as they do on Earth - namely, that it will be proportional to the mass multiplied by the square of the distance to that mass.

Experiencing a different weight on the Moon is not the same as experiencing different gravity.

Your statement is quite misleading.
 
  • #62
DaveC426913 said:
A person on the Moon experiences gravity exactly the same as they do on Earth - namely, that it will be proportional to the mass multiplied by the square of the distance to that mass.

Experiencing a different weight on the Moon is not the same as experiencing different gravity.

Your statement is quite misleading.

The Gravity constant is defined by the freefall acceleration in a vacuum of a body near the surface of the Earth. (m/s^2) I did not say anything at all about weight. This gravity constant is different on the Moon than on the Earth and as such the person on the moon certainly does experience different gravity than the person on Earth. The force is stronger on the Earth than it is on the moon. The person on the moon experiences gravity towards the Moon's center of mass, the person on Earth experience gravity towards Earth's center of mass. If this wasn't the case the person on the Moon would fall off and fall back to Earth.
 
  • #63
ttmark said:
The Gravity constant is defined by the freefall acceleration in a vacuum of a body near the surface of the Earth. (m/s^2)
That is not the gravitational constant, that is the acceleration due to gravity at the surface of the Earth (signified by "g").

The gravitational constant is 6.673e_11 m^3/kgs^2(signified by G) and this is the same for all masses. You use the gravitational constant, the mass and radius of the body to find the acceleration due to gravity at that body's surface.
 
  • #64
Janus said:
That is not the gravitational constant, that is the acceleration due to gravity at the surface of the Earth (signified by "g").

It is the gravity constant for Earth. I see you agree that the gravity constant for the moon is something else entirely.
 
  • #65
ttmark said:
It is the gravity constant for Earth. I see you agree that the gravity constant for the moon is something else entirely.

It's not a constant. You can tell this because it's not constant. :wink:

It is simply the value of a force at a given location, and it has a different value at a location three feet to your left or three feet above your head.

The gravity constant G is the same everywhere on the Earth, on the Moon, and, if we understand correctly, everywhere else in the universe.
 
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  • #66
Do you mean g or G?
 
  • #67
sophiecentaur said:
Do you mean g or G?

That is precisely ttmark's confusion.


ttmark, this would not be under discssuon at all if you would care to read up a little about G versus g. The first paragraph of Wiki will do for now:

The gravity of Earth, denoted g, refers to the acceleration that the Earth imparts to objects on or near its surface. ... It has an approximate value of 9.81 m/s2, which means that, ignoring air resistance, the speed of an object falling freely near the Earth's surface increases by about 9.81 metres per second every second. This quantity is informally known as little g (contrasted with G, the gravitational constant, known as big G).
http://en.wikipedia.org/wiki/Gravity_of_Earth


g on Earth is no more a constant than is v in a moving car.
 
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  • #68
DaveC426913 said:
That is precisely ttmark's confusion.

We all know this, there is no confusion on my part. You can use the universal gravity constant if you want but it doesn't change the fact that a person on the moon experiences gravity different than a person on Earth. There is more gravity on Earth than the Moon and each is towards their own center of mass.
 
  • #69
ttmark said:
We all know this, there is no confusion on my part.
You have just figured it out now - after we practically beat it into you. Don't make me quote the number of times you mixed them up.

ttmark said:
You can use the universal gravity constant if you want but it doesn't change the fact that a person on the moon experiences gravity different than a person on Earth. There is more gravity on Earth than the Moon and each is towards their own center of mass.
Of what relevance is that?
Here:
https://www.physicsforums.com/showpost.php?p=3336689&postcount=58
you claim it changes all the time and then call it circular reasoning.

Our measurement of G did not depend on g, so why have you been trying so hard to claim that there's circular reasoning?

That's a rhetorical queation. We know the answer. You were confused. Again, don't make me quote you.
 
  • #70
DaveC426913 said:
You have just figured it out now - after we practically beat it into you. Don't make me quote the number of times you mixed them up.
That's a rhetorical queation. We know the answer. You were confused. Again, don't make me quote you.

As you can see in my post, "As you are aware many things can make you experience a different gravity constant". Notice gravity is lower case and referencing an experience felt by a person. This is clearly written referring to a point of reference of someone on Earth.

Your personal attacks are unneeded and against forum rules and will be ignored. Please read "Guidelines on Langauge and Attitude:"
 

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