But the libration movement of the Moon, as seen from Earth, and the fact that the Moon's rotation rate and revolution rate are not constantly in perfect sync, only after a long period of time, is not an explanation or proof of the Moon's own axial rotation.
It refutes Tesla's notion that the Moon is locked into a matrix as it revolves around the Earth, and that all collections of points within that matrix rotate in concert with the Moon's axial rotation. As a solid body in the near absence of friction the Moon maintains both its axial rotation rate and its axial rotational momentum. The Moon's orbital angular velocity around the Earth varies as its distance from Earth varies in its eccentric orbit. However, its orbital angular momentum is maintained since distance from Earth is a factor. The two forms of angular momentum exist and are distinct. Indeed, a tidal consideration maintains the Moon's orbital angular velocity and its axial rotational velocity at the same value when averaged over a sufficient period of time. But that does not mean that two separate forms of angular momentum do not exist in this case.

2. It's not as convenient as doing it in this thread... but I'm continuing to discuss the moon rotation issue with Sadang through PM's... and I'll let you all know if one of us changes our mind

3. Originally Posted by P Timmy
It's not as convenient as doing it in this thread... but I'm continuing to discuss the moon rotation issue with Sadang through PM's... and I'll let you all know if one of us changes our mind
As I think I understand it, his argument is that in the special case of an orbiting body in synchronous rotation, the body is not “really” or “actually” rotating around its axis of symmetry but only is giving the illusion of doing so as seen from certain points of view. I remain confident in my opinion that this is a philosophical issue of what constitutes reality, and that an answer to it one way or the other is of no consequence as an exercise in physics. Such an exercise is concerned with developing a mathematical model that enables accurate calculations and predictions of the body’s motion and related attributes.

Suppose we mount a ball rigidly on the edge of a rotating wheel. If we so wished we could say that the ball is not “really” rotating around its own axis of symmetry but rather is “actually” part of the wheel which is rotating around its own center. Starting with the definition of angular momentum for an infinitesimal increment of mass we can calculate the integrated amount for the ball in either of two ways. One way is to integrate over the extent of the ball purely as a function of the position with respect to the center of the wheel. I think that would be doing it the hard way. It is much easier to analyze the ball as rotating around its own center and integrate the angular momentum from that rotation. Then we add that to the amount a point mass at the center of the ball would have from the orbital component of the motion, using the same total mass. I was taught in elementary physics that such a combination is mathematically valid, and I think the aforementioned parallel axis theorem validates it.

Guess what: The calculated magnitude of the ball’s share of the angular momentum of the system is going to be the same either way. I tested it with a simplified system consisting of two points on the wheel, aligned with its center, and I am confident that it holds for the general case of an extended body.

If you disagree with Sadang's argument I recommend standing your ground. If he rationalizes by insisting that no one has refuted him and "declares victory", so be it. The effect of such an outcome on the practice of good physics is zilch.

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Originally Posted by P Timmy
...I'm continuing to discuss the moon rotation issue with Sadang through PM's... and I'll let you all know if one of us changes our mind
With all due respect, this is a discussion board, and he doesn't want to participate in this discussion.

Based on that, I don't care what his opinion is, if he refuses to "back it up" with evidence.

Originally Posted by Hornblower
If he rationalizes by insisting that no one has refuted him and "declares victory", so be it.
It is accepted by mainstream science that the Moon rotates...if someone disagrees, the onus is on them to prove themselves correct, not on mainstream science to prove them wrong.
Last edited by R.A.F.; 2012-May-23 at 08:03 PM. Reason: changed wording last sentence for clarity.

5. Originally Posted by Hornblower
If he rationalizes by insisting that no one has refuted him and "declares victory", so be it. The effect of such an outcome on the practice of good physics is zilch.
I found the discussion with him in this thread to be interesting... but it's true... the practice of good physics will live on whether anyone continues to make an effort to explain the mainstream view to Sydang or not.

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Originally Posted by Jeff Root

I repeat: The person for you to converse with is
Gerald Kelleher, also known online as Oriel36. He is
the one guy you want to talk to.

-- Jeff, in Minneapolis
Well,if it isn't Jeff.

Barely a week after the magnificent planetary phase of Venus and a week before the June Solstice event where the polar coordinates,acting like a beacon for the orbital behavior of the Earth,turn in a circle/cycle to their maximum distance from the circle of illumination.

The moon doesn't spin and you all should know better than this,that ideology was a throwaway statement only made by Newton barely a few sentences after he states Venus rotates in 23 hours and the Earth to the circumpolar stars in 24 hours ! -

There is no need to batten down the hatches and go into moderative spasms,the idea is that the Earth does turn once to the central Sun coincident with its orbital period and aside from the daily rotational cycle while the moon keeps the same face to us in its monthly lunar cycle - simply walk around an object with an outstretched arm and you will get the picture.Intrinsic rotation refers to variations in latitudinal speeds and I am not going to dignify a response explaining the difference between orbital motion and daily rotation,the moon has the former but not the latter.
Last edited by gkell1; 2012-Jun-16 at 09:09 PM.

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total angular momentum of the body in the synchronous rotation:
, where: w - spin
Thus the spin of the body is probably zero.

8. Originally Posted by Hetman
total angular momentum of the body in the synchronous rotation:
, where: w - spin
Thus the spin of the body is probably zero.
The body is the earth's moon? What does your equation mean?

The moon "spins" once every 27+ days.

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Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

s - spin (rotation around its own axis)
'w' - orbital angular velocity
for s = 0 is the lowest energy.

Anyway, this is an old problem: revolution and rotation.

10. Originally Posted by Hetman
Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

s - spin (rotation around its own axis)
'w' - orbital angular velocity
for s = 0 is the lowest energy.

Anyway, this is an old problem: revolution and rotation.
I stand by my reasoning in post 63, and your posts have done nothing to shake my confidence. Can you show us, in appropriate mathematical detail, what you think is wrong, if any, and why you think so?

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Maybe it is spinning ... with minimum energy.

12. Originally Posted by Hetman
Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

s - spin (rotation around its own axis)
The moon is spinning on its own axis, that's irrefutable. The star field cycles once per 27+ days.

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Originally Posted by grapes
The moon is spinning on its own axis, that's irrefutable.
Do they convey additional information? If so, what
information?

-- Jeff, in Minneapolis

14. Originally Posted by Jeff Root
Do they convey additional information? If so, what
information?
That's pretty much the bone of contention--is it spinning on its own axis, or someone else's axis.

I think the point that you are making is that it doesn't matter--they're essentially equivalent. But some assert one, and deny the other.

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So maybe the question to ask is "What is an axis?"

-- Jeff, in Minneapolis

16. Have we answered "what is spinning?" already? If not, let's do that one first.

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When you rotate the ball on the line, then it does not spin.
Only detached from the rope, or when it is free, it can spin.

A player running around the stadium is not spinning.

It is even more controversial case: rolling (without sliding).
Here the body rotates about an axis, which is on its periphery.

This is probably the famous half-spin.

18. Originally Posted by Hetman
When you rotate the ball on the line, then it does not spin.
Only detached from the rope, or when it is free, it can spin.
The problem with that kind of reasoning, is that it leads people to imagine some weird unknown force that is keeping one face of the Moon always towards Earth, as though the Moon were that ball. What's the string?

(e.g. do you claim that the tidal/gravitational forces that science thinks has over time made the rotation of the Moon match it's orbit of the Earth, is actually strong enough to simply "hold" one face of the Moon towards Earth, the way your string holds that ball?)

Originally Posted by Hetman
A player running around the stadium is not spinning.
I'd say that runner is rotating, around an axis down through the top of their head, while also translating that axis.

The force that causes both the rotation and translation is supplied by their feet against the track.

If they didn't apply a force to rotate, they'd run off the track.

(Not being free from friction, they don't simply continue to rotate the way they would, floating space.)

Originally Posted by Hetman
It is even more controversial case: rolling (without sliding).
Here the body rotates about an axis, which is on its periphery.

This is probably the famous half-spin.
So if a bowling ball rolls down the lane, where do you claim the axis of rotation is?

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Originally Posted by pzkpfw
The problem with that kind of reasoning, is that it leads people to imagine some weird unknown force that is keeping one face of the Moon always towards Earth, as though the Moon were that ball. What's the string?

(e.g. do you claim that the tidal/gravitational forces that science thinks has over time made the rotation of the Moon match it's orbit of the Earth, is actually strong enough to simply "hold" one face of the Moon towards Earth, the way your string holds that ball?)
Why is that weird?
After all the situation of the Moon is identical with the case of the ball on the line.

The moon is maintained (by something) in its present state - that is synchronization.

Originally Posted by pzkpfw
So if a bowling ball rolls down the lane, where do you claim the axis of rotation is?
On the floor.
During the rolling the axis of rotation is at the point of support.

20. Originally Posted by Hetman
Why is that weird?
After all the situation of the Moon is identical with the case of the ball on the line.

The moon is maintained (by something) in its present state - that is synchronization.
My bold.

No. The standard view is that the Moon rotates. As with anything in space, no force is needed to make it continue to rotate. (Though, the small tidal/gravitational force has affected the rotation over a long period of time).

If, in your view, there is a force being applied to it to make it face Earth - that's quite a different thing. If the natural inclination of the Moon was to not rotate, how much force must be being applied to "maintain" it's current effective rotation?

Originally Posted by Hetman
On the floor.
During the rolling the axis of rotation is at the point of support.
So the axis of rotation is at the point of contact between the outside of the ball and the floor?

That means the axis of rotation "slides past" the circumference. That is another odd way of looking at it.

Why do you reject that the centre of the ball in this case is the axis of rotation? Why does it instead need to be the place where the force that makes it rotate is applied?

If I pitch a baseball it spins as it flies towards the batter. I've applied my forces to the outside of that ball - would you again say the axis of rotation is at the outside of that ball?

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Originally Posted by pzkpfw
No. The standard view is that the Moon rotates. As with anything in space, no force is needed to make it continue to rotate. (Though, the small tidal/gravitational force has affected the rotation over a long period of time).

If, in your view, there is a force being applied to it to make it face Earth - that's quite a different thing. If the natural inclination of the Moon was to not rotate, how much force must be being applied to "maintain" it's current effective rotation?
And how much force must be being applied to maintain rotation of the ball on line?

When the rotation of the Moon is decreasing, then it is increased, and when the rising vice versa - is reduced.

I do not know whether Foucault pendulum will keep the direction of motion on the Moon, but it is not excluded.
The pendulum will be affected by the same forces, which permanently synchronizes the Moon.

Originally Posted by pzkpfw
Why do you reject that the centre of the ball in this case is the axis of rotation? Why does it instead need to be the place where the force that makes it rotate is applied?
In this way, you get just one simple rotary motion rather than a combination of several movements (more redundant equations and variables).

Originally Posted by pzkpfw
If I pitch a baseball it spins as it flies towards the batter. I've applied my forces to the outside of that ball - would you again say the axis of rotation is at the outside of that ball?
It depends on whether it is free or not.
And remember: the simpler the better, but seriously, not only in appearance.

22. Originally Posted by Hetman
... In this way, you get just one simple rotary motion rather than a combination of several movements (more redundant equations and variables).
Eh? The standard view is that the ball is rotating and translating. The axis of rotation is the centre of the ball, and that axis moves in the direction of the ball.

In what way is your view simpler?

Originally Posted by Hetman
It depends on whether it is free or not.
And remember: the simpler the better, but seriously, not only in appearance.
It depends if it's free or not? Again, how is that simpler?

For that matter: which is simpler...
A: That the Moons rotation period now matches its orbit period.
B: Some unknown force is causing one face of the Moon to always point towards Earth.

23. Originally Posted by Hetman
Originally Posted by pzkpfw
So if a bowling ball rolls down the lane, where do you claim the axis of rotation is?
On the floor.
During the rolling the axis of rotation is at the point of support.
Um...no. As one who practiced a great deal to develop a consistent hook, I can say that a bowling ball's axis of rotation is not necessarily coincident to the point of contact with the floor. In fact, spinning about a nearly vertical axis like that is just about the least effective way of acheiving a hook. With variation between bowlers, the axis of a hooking ball is much closer to being parallel to the floor and roughly in line with the direction of travel at the point of release. This video demonstrates it pretty nicely. Watch the large white dot just after release. It's pretty darn close to the initial axis of rotation...which changes during the roll, most likely due to the ball being balanced for hook.

24. Originally Posted by Hetman
The pendulum will be affected by the same forces, which permanently synchronizes the Moon.
In other words, you think that the pendulum would move with the moon, and not precess relative to the moon? That's certainly wrong.

From my point of view, anyone who says the rotation axis cannot be the center of the bowling ball just doesn't understand the physics. Same for whether the rotation axis can be on the edge of the ball.

25. Originally Posted by grapes
... From my point of view, anyone who says the rotation axis cannot be the center of the bowling ball just doesn't understand the physics. Same for whether the rotation axis can be on the edge of the ball.
It's a bit like saying the axis of rotation of your cars' wheel (let's assume an undriven wheel, for the heck of it) is not the axle, but the point of contact with the road.

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Originally Posted by pzkpfw
Eh? The standard view is that the ball is rotating and translating. The axis of rotation is the centre of the ball, and that axis moves in the direction of the ball.

In what way is your view simpler?
It is simpler because natural.

This is best seen on an inclined plane:
we put the ball, and the force of gravity would normally rotate it around the fulcrum.

The situation identical to that of overturning a pencil, which we put almost vertically (center of gravity is outside the base).

It is simple rotation around a single point - the support,
which in the case of circular objects leads to a continuous movement - a ball can not roll over.

The round object can be maintained in place on an inclined surface (without attachment, of course)?
This is a very fun exercise, often appears in textbooks to the mechanics.

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Originally Posted by grapes
In other words, you think that the pendulum would move with the moon, and not precess relative to the moon? That's certainly wrong.
The forces on the pendulum usually will be different in each half period, due to the additional forces of the Earth (it oscillates asymmetrically).

Therefore, this asymmetry probably would change the direction of oscillation, the oscillation plane will change - no longer would be fixed relative to the stars.

There is only one good plane, ie one in which the pendulum would be symmetrical.
And perhaps the pendulum will just converge to this plane - sync.

Originally Posted by grapes
From my point of view, anyone who says the rotation axis cannot be the center of the bowling ball just doesn't understand the physics. Same for whether the rotation axis can be on the edge of the ball.
Very good. There is no man on earth who understands physics.

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Originally Posted by pzkpfw
It's a bit like saying the axis of rotation of your cars' wheel (let's assume an undriven wheel, for the heck of it) is not the axle, but the point of contact with the road.
Only a "bit"?...I would say exactly like...

29. Originally Posted by Hetman
It is simpler because natural.

This is best seen on an inclined plane:
we put the ball, and the force of gravity would normally rotate it around the fulcrum.

The situation identical to that of overturning a pencil, which we put almost vertically (center of gravity is outside the base).

It is simple rotation around a single point - the support,
which in the case of circular objects leads to a continuous movement - a ball can not roll over.

The round object can be maintained in place on an inclined surface (without attachment, of course)?
This is a very fun exercise, often appears in textbooks to the mechanics.
That only supplies a momentary view of the effect that causes the ball to roll. There's no way you can apply that (alone) to the ball rolling along the lane.

The ball is clearly rotation and translating. Your picture is not the whole story, because point P can not stay at point P.

You seem to have that image off Wikipedia - can you point out that page it's used in?

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Originally Posted by pzkpfw
That only supplies a momentary view of the effect that causes the ball to roll. There's no way you can apply that (alone) to the ball rolling along the lane.
When that moment ends?
The axis of rotation is permanently in the same place.

Originally Posted by pzkpfw
The ball is clearly rotation and translating. Your picture is not the whole story, because point P can not stay at point P.
Some reminiscences of the early 20th century?

This point can not escape, nor the axis break.

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

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