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P Timmy
2012-Mar-25, 04:37 AM
I was discussing moon rotation with a guy just last week (and invited him here to discuss it)... who is convinced that the moon only revolves around the earth and does not rotate on an internal axis.!!!
For any who might still think the moon does not rotate... below is an animation which shows that the moon rotates one time during one revolution of the earth.!!!

Note:::
The red dot rotates one time around its green dot axis during one revolution of the earth.!!!

http://www.bautforum.com/attachment.php?attachmentid=16613&d=1332900943

antoniseb
2012-Mar-25, 12:23 PM
This sense that it doesn't rotate is common among people who look at it but don't think about it. I like to point out that someone patient sitting on the Moon at one place will see some particular star in the sky rise, move across the sky, set, and then rise again 27.3 Earth-days later... which says the same thing as your diagram, but sells the idea to a different subset of people.

P Timmy
2012-Mar-26, 05:42 AM
This sense that it doesn't rotate is common among people who look at it but don't think about it. I like to point out that someone patient sitting on the Moon at one place will see some particular star in the sky rise, move across the sky, set, and then rise again 27.3 Earth-days later... which says the same thing as your diagram, but sells the idea to a different subset of people.

For sure moon rotation is quite the puzzler for some people... and for some people (so far)... I haven't found any solution that sells them the idea... but I find it interesting to try and fun making new animated gifs to support the fact that the moon rotates on an internal axis... plus I've learned new and interesting things along the way.!!!

In the animated gif below... no one disagrees that the object in the center is rotating on its axis... and lets say that the object in the center takes 27.3 days to complete one rotation.!!!

It can also be seen that the object in the center and the object in orbit are interchangeable... so just like our moon... the object in orbit also completes one rotation every 27.3 days... the same length of time it takes to complete one revolution.!!!

http://www.bautforum.com/attachment.php?attachmentid=16614&d=1332902697

ShinAce
2012-Mar-26, 02:49 PM
If it ain't tied down, it will rotate!

Imagine a ball on the end of a string. Most people can imagine the string as gravity and the ball as the moon. If you start spinning where you're standing, the ball flies around in a circle. It orbits, but most would say it does not revolve. They can argue that if it revolved, it would wind up the string around itself, which doesn't happen.

Likewise, can you pick a frame where the moon does not rotate? Maybe one where a spot on the moon faces the same direction as a sunspot. But the sun rotates, so that's no good. How about a point where the stars are pretty much stationary from the moon. But then the galaxy is in rotation, so the moon must still rotate. With motion being relative, and rotational motion being a major headache at that, it's very easy to just stick to your guns and say the moon isn't rotating.

The main point I hold on to is that the moon's period is a special case. If it starts to rotate faster, tidal forces will bring it back to where it is now. If it tries to rotate slower, again tidal forces bring it back. It very well does have a certain equilibrium(resonance) to it, which I do not associate with rotation by itself. It's easy to imagine that tidal foces have slowed the moon's rotation to the point where it can't anymore. It becomes tempting to say the moon doesn't have a day/night because of rotation, but because of its orbit instead. Which is wrong, but alluring.

P Timmy
2012-Mar-26, 06:21 PM
Imagine a ball on the end of a string. Most people can imagine the string as gravity and the ball as the moon. If you start spinning where you're standing, the ball flies around in a circle.

I performed the ball on a string experiment... and if the ball detaches from the string... the balls angular momentum (due to rotation) is retained and the ball will rotate on its axis as it flies off in a "straight" line... just as the moon would continue to rotate once every 27.3 days (as it orbits the sun) if the earth (and its gravity) suddenly disappeared.!!!

Hornblower
2012-Mar-26, 10:38 PM
I don't think anyone who observes a proper demonstration of the motion denies the fact that the Moon continuously changes the direction it is facing with respect to the fixed stars as it goes around its orbit. Those who deny rotation seem to be hung up on quibbling with words in defining the components of the motion.

Jens
2012-Mar-27, 12:43 AM
I don't think anyone who observes a proper demonstration of the motion denies the fact that the Moon continuously changes the direction it is facing with respect to the fixed stars as it goes around its orbit. Those who deny rotation seem to be hung up on quibbling with words in defining the components of the motion.

That's my impression as well. And people definitely will quibble about it. In a sense it seems equivalent to arguing that for example, the moon doesn't really go around the earth because the earth is moving around the sun and the moon is doing a sort of oscillating movement with regard to the sun, since its orbital speed around the earth is less than the earth's orbital speed around the sun, hence it can never go around the earth. It's fallacious, but it has a certain allure to it.

P Timmy
2012-Mar-27, 05:10 AM
I don't think anyone who observes a proper demonstration of the motion denies the fact that the Moon continuously changes the direction it is facing with respect to the fixed stars as it goes around its orbit.

Yes that doesn't seem to be an issue.!!!

Those who deny rotation seem to be hung up on quibbling with words in defining the components of the motion.

Maybe some of those people will show up and present their non rotating moon quibbles and then we might come to a meeting of the minds on the issue of whether or not the moon rotates on an internal axis.!!!

The last guy I discussed the issue with claimed that the "hammer" (as in track and field events) doesn't rotate when released because like the moon... it also has no angular momentum.!!!

Below is an animated gif of how he thinks a hammer would fly through the air after being released.!!!

(Refresh to repeat the animation)

http://www.bautforum.com/attachment.php?attachmentid=16615&d=1332904853

Jens
2012-Mar-27, 07:28 AM
There are probably others, but here is an earlier thread (http://www.bautforum.com/showthread.php/86156-Technically-Speaking-Does-the-Moon-Rotate?highlight=moon+rotation) where it came up. There are probably others as well.

Hornblower
2012-Mar-27, 12:44 PM
Yes that doesn't seem to be an issue.!!!

Maybe some of those people will show up and present their non rotating moon quibbles and then we might come to a meeting of the minds on the issue of whether or not the moon rotates on an internal axis.!!!

The last guy I discussed the issue with claimed that the "hammer" (as in track and field events) doesn't rotate when released because like the moon... it also has no angular momentum.!!!

Below is an animated gif of how he thinks a hammer would fly through the air after being released.!!!(Refresh to repeat the animation)

http://ptim.heliohost.org/CurrentDisplay/HammerZeroRotation.gifMy bold. It appears that he has a passing acquaintance with physics and is applying it badly, and the animation is crude and simplistic.

While the thrower is swinging the hammer, it is moving much as the Moon does. When it is released, the ball continues to rotate initially, but atmospheric drag on the chain and handle will stop it or at least slow it down. I would be interested in seeing good closeup slow motion video of the action. I have never had a good look at a track meet. My educated guess is that the ball will be oscillating with the chain fluttering like a flag in a breeze.

antoniseb
2012-Mar-27, 04:47 PM
I don't think the wind resistance would have much impact on the angular momentum of the ball at the end of the chain, but that ball is only spinning at roughly one RPS and would only have time to rotate maybe two or three times before hitting the dirt again. It's not like a spinning fastball in baseball where the rotation is obvious at a glance.

Jeff Root
2012-Mar-27, 05:27 PM
The animation isn't animated for me.

Edit: Never mind, I got it. Straight out from the center, eh?

of years ago in which the poster was adamant about the Moon
either not rotating or rotating only because it is going around in
a circle. The animations showed a rotating geologist's hammer.
I intended to present the animations one at a time and ask the
poster whether the hammer was rotating in each case, but the
thread was closed just after I got started.

I agree with antoniseb that the rotation of the throwing hammer
would hardly be affected by air resistance at all. I'd expect more
like 3 or 4 rotations per second.

-- Jeff, in Minneapolis

P Timmy
2012-Mar-27, 08:38 PM
There are probably others, but here is an earlier thread (http://www.bautforum.com/showthread.php/86156-Technically-Speaking-Does-the-Moon-Rotate?highlight=moon+rotation) where it came up.

The last guy I discussed the issue with claimed that the "hammer" (as in track and field events) doesn't rotate when released because like the moon... it also has no angular momentum.!!!

Below is an animated gif of how he thinks a hammer would fly through the air after being released.!!!

(Refresh to repeat the animation)
http://ptim.heliohost.org/CurrentDisplay/HammerZeroRotation.gif

...the animation is crude and simplistic.

Well in my defense... ALL my animations are kinda rough :-)
Below is another gif that roughly demonstrates the correct motions of a hammer after its release.!!!

("refresh" to animate gif)
http://www.bautforum.com/attachment.php?attachmentid=16619&d=1332906710

Hornblower
While the thrower is swinging the hammer, it is moving much as the Moon does. When it is released, the ball continues to rotate initially, but atmospheric drag on the chain and handle will stop it or at least slow it down. I would be interested in seeing good closeup slow motion video of the action. I have never had a good look at a track meet. My educated guess is that the ball will be oscillating with the chain fluttering like a flag in a breeze.

The effect isn't as dramatic as you imagined but your educated guess is on target.!!!
Below is the link "the guy" used to support his argument that a hammer does not rotate after it's released... and yet... 30 seconds into the video... the hammer and chain can be seen to rotate after being released... and 1:50 into the video... slow motion shows the hammer and chain still rotating as they fly down the field... but toward the end of its flight the ball does appear to be a bit lower than the handle due to wind resistance having a greater effect on the chain and handle.!!!

grapes
2012-Mar-28, 03:04 AM
Now try this one:

:)

P Timmy
2012-Mar-28, 05:12 AM
Now try this one:
:)

Ah yes... that's my friend Ken Dine who started that thread... the guy I recently invited to come here and discuss moon rotation... but since He's already been here and done that... I guess that's why he didn't show up again.!!!

So far I've only read part of his thread but I enjoyed it very much and will finish it as time permits... and as his thread demonstrates... He's a smart guy and He's not just yanking chains... He's sincere about his non-rotating moon beliefs.!!!

Hornblower
2012-Mar-28, 09:27 AM

Well in my defense... ALL my animations are kinda rough :-)
Below is another gif that roughly demonstrates the correct motions of a hammer after its release.!!!

("refresh" to animate gif)
http://www.bautforum.com/attachment.php?attachmentid=16619&d=1332906710

The effect isn't as dramatic as you imagined but your educated guess is on target.!!!
Below is the link "the guy" used to support his argument that a hammer does not rotate after it's released... and yet... 30 seconds into the video... the hammer and chain can be seen to rotate after being released... and 1:50 into the video... slow motion shows the hammer and chain still rotating as they fly down the field... but toward the end of its flight the ball does appear to be a bit lower than the handle due to wind resistance having a greater effect on the chain and handle.!!!

That Olympic video does appear to show for sure that the ball is indeed rotating and whirling the chain around. I can see now that a lot more time in flight would be needed for the air drag to stop it.

grapes
2012-Mar-28, 10:00 AM
Ah yes... that's my friend Ken Dine who started that thread... the guy I recently invited to come here and discuss moon rotation... but since He's already been here and done that... I guess that's why he didn't show up again.!!!
He's the guy that you mention in the OP, post #1? Interesting.

So far I've only read part of his thread but I enjoyed it very much and will finish it as time permits... and as his thread demonstrates... He's a smart guy and He's not just yanking chains... He's sincere about his non-rotating moon beliefs.!!!No, finish the thread.

Jeff Root
2012-Mar-28, 10:39 AM
Lemme say what I never got to say in the thread grapes just
linked to. The first animation of the rotating geological hammer
had the center of rotation at what looked like might be the center
of mass. Each succeeding animation had the center of rotation
farther and farther away from that point. After a few iterations,
the center of rotation moved beyond the end of the handle, the
way it would actually be swung by someone using it. At some
point the nutcase would say the hammer was no longer rotating,
and I would ask whether the rotation suddenly vanished at that
point, or if successive animations depicted progressively less
and less rotation.

-- Jeff, in Minneapolis

P Timmy
2012-Mar-30, 05:45 AM
The last guy I discussed the issue with claimed that the "hammer" (as in track and field events) doesn't rotate when released because like the moon... it also has no angular momentum.!!!

Below is an animated gif of how he thinks a hammer would fly through the air after being released.!!!

(Refresh to repeat the animation)

http://www.bautforum.com/attachment.php?attachmentid=16615&d=1332904853

Straight out from the center, eh?

Yep... but after watching a hammer throw video he did acknowledge there was a wobble motion when the hammer was released... but he explained that the wobble comes from the hammer thrower jerking on the handle as it's being released.!!!

Early on in the discussion (about 5 years ago) I told him about my experiment of attaching a two foot length of string to a tennis ball and then swinging the ball in a circle overhead... and when I released the string the ball rotated as it flew off in a "straight" line... and finally he agreed to perform the experiment but he used a tetherball attached to its eight foot rope... and he reported that the ball did make a jerking motion when he released the rope but it didn't fully rotate and continued on with the rope trailing behind.!!!

I explained to him that I used the smallest string I could find (dental floss) so it would have less effect on the angular momentum of the tennis ball... and that the long rope he used was too much drag for the angular momentum of the tetherball to overcome... but he said that was nonsense.!!!

It's to bad he refused to perform a proper experiment... because he agreed that if the ball rotated when the string was released... that meant it had angular momentum and that the moon also had angular momentum and rotated.!!!

Hornblower
2012-Mar-30, 12:00 PM
When making an analogy between the Moon and a tethered ball, whatever happens in the real world when the tether is released, such as in the hammer throw, is irrelevant to the question about the Moon's rotation, because the Moon is not released. We should be concerned only with what the ball is doing while the tether is being held and swung.

Jeff Root
2012-Mar-30, 12:29 PM
I think that releasing the ball is intended to show what the ball
had been doing before it was released: rotating. If we are dealing
with the same person-like entity as in the earlier BAUT thread,
then the question is not whether the Moon is rotating, but whether
it can be *shown* that the Moon is rotating. Sort of like trying to
prove that you exist.

-- Jeff, in Minneapolis

P Timmy
2012-Mar-30, 01:48 PM
When making an analogy between the Moon and a tethered ball, whatever happens in the real world when the tether is released, such as in the hammer throw, is irrelevant to the question about the Moon's rotation, because the Moon is not released. We should be concerned only with what the ball is doing while the tether is being held and swung.

The relevance of the tennis ball experiment is to demonstrate what the moon is doing in the real world.!!!

Because the moon has angular momentum... if the earth suddenly disappeared the moon would be released from its tether of earth's gravity and rotate once every 27.3 days as it orbits the sun... which would be very clear visual proof that an object in synchronous rotation (such as the moon) does have angular momentum and therefore rotates on an internal axis... but since we can't make the earth's gravity disappear to perform such an experiment... we can substitute a tethered tennis ball for the moon and then we can observe that visual evidence.!!!

Jerry
2012-Apr-17, 04:11 AM
If the moon is painted on a cylinder wall, the moon need not rotate to keep the same face pointed toward the earth all the time...This allows the sun to rotate about the Earth, too:)

grapes
2012-Apr-17, 08:02 AM
If the moon is painted on a cylinder wall, the moon need not rotate to keep the same face pointed toward the earth all the time...This allows the sun to rotate about the Earth, too:)In this scenario, are the sun and moon on different cylinders? Which cylinder moves, the sun cylinder or the moon cylinder? :)

If you can stand on the "surface" and watch the star fields go by, in regular and repeating progression, the body is rotating. So...which cylinder are the stars on???

Centaur
2012-Apr-21, 12:42 AM
That's my impression as well. And people definitely will quibble about it. In a sense it seems equivalent to arguing that for example, the moon doesn't really go around the earth because the earth is moving around the sun and the moon is doing a sort of oscillating movement with regard to the sun, since its orbital speed around the earth is less than the earth's orbital speed around the sun, hence it can never go around the earth. It's fallacious, but it has a certain allure to it.

That's not really a far out way of looking at the situation and perhaps not fallacious. The Moon is the only planetary satellite whose motion relative to the Sun is continuously concave. It could be said that both the Earth and Moon orbit the Sun while perturbing each other from more perfectly elliptical heliocentric orbits. The way we more commonly consider the situation is also quite acceptable. The latter is the basis of how we analytically (i.e. without numerical integration) calculate the Moon's motion, but the presence of the Sun makes the method immensely complex. Newton complained it gave him headaches.

2012-May-14, 07:49 AM
Timmy, in your first animation, the Moon is not rotating around its own axial center of rotation wrt the center of revolving (or to any point internal to the circle of revolution of the Moon), but it SEEMS to have its own axial rotation wrt the Sun (or to any point external to the circle of revolution of the Moon). So, in the Earth-Moon system, I clearly sustain that the Moon does not have its own axial rotation movement. I also sustain, that outside of the same Earth-Moon system, the Moon has ONLY an APPARENT, not a REAL own axial rotation movement.

- 1919 - Electrical Experimenter - Nikola Tesla - Famous Scientific Illusions (http://scribd.com/doc/90144454/1919-Electrical-Experimenter-Nikola-Tesla-Famous-Scientific-Illusions)
- 1919 - Electrical Experimenter - Nikola Tesla - Moon's Rotation (http://scribd.com/doc/90097922/1919-Electrical-Experimenter-Nikola-Tesla-Moon-s-Rotation)

I invite everyone who understand what is general relativity, and can analyze the motion of an object in different reference systems, and to expose the arguments for or against those supported by me.

P Timmy
2012-May-14, 02:08 PM
Timmy, in your first animation, the Moon is not rotating around its own axial center of rotation wrt the center of revolving (or to any point internal to the circle of revolution of the Moon)...

Welcome to the group sadang... hopefully you will find the people here willing to hear your arguments and discuss in a respectful manner.
I have to do other things now but I will respond as soon as I can to the issues you raise.

Jeff Root
2012-May-14, 02:56 PM

As I recommended in the other thread, you need to
contact Gerald Kelleher, who often goes by the name
Oriel36. He is the one person you need to discuss
this with. He used to post on sci.astro and I have
seen references to him on the web.

-- Jeff, in Minneapolis

Jens
2012-May-15, 01:20 AM
Timmy, in your first animation, the Moon is not rotating around its own axial center of rotation wrt the center of revolving (or to any point internal to the circle of revolution of the Moon), but it SEEMS to have its own axial rotation wrt the Sun (or to any point external to the circle of revolution of the Moon). So, in the Earth-Moon system, I clearly sustain that the Moon does not have its own axial rotation movement. I also sustain, that outside of the same Earth-Moon system, the Moon has ONLY an APPARENT, not a REAL own axial rotation movement.

I'm not quite clear on what you're trying to say, but let me ask you a question. Suppose you hold a bicycle wheel in your hands and make it spin. We all agree it has a rotation, I think. Now, if you put it on the ground and let it go so that it starts moving, is it still rotating around its own center of rotation, or is it no longer rotating?

P Timmy
2012-May-15, 02:41 AM
Timmy, in your first animation, the Moon is not rotating around its own axial center of rotation wrt the center of revolving (or to any point internal to the circle of revolution of the Moon), but it SEEMS to have its own axial rotation wrt the Sun (or to any point external to the circle of revolution of the Moon). So, in the Earth-Moon system, I clearly sustain that the Moon does not have its own axial rotation movement. I also sustain, that outside of the same Earth-Moon system, the Moon has ONLY an APPARENT, not a REAL own axial rotation movement.

Well lets begin with this. In the animation below... do you agree that the object in the center is rotating on an internal axis and has angular momentum?

http://www.bautforum.com/attachment.php?attachmentid=16614&d=1332902697

Hornblower
2012-May-15, 03:56 AM
Timmy, in your first animation, the Moon is not rotating around its own axial center of rotation wrt the center of revolving (or to any point internal to the circle of revolution of the Moon), but it SEEMS to have its own axial rotation wrt the Sun (or to any point external to the circle of revolution of the Moon). So, in the Earth-Moon system, I clearly sustain that the Moon does not have its own axial rotation movement. I also sustain, that outside of the same Earth-Moon system, the Moon has ONLY an APPARENT, not a REAL own axial rotation movement.

- 1919 - Electrical Experimenter - Nikola Tesla - Famous Scientific Illusions (http://scribd.com/doc/90144454/1919-Electrical-Experimenter-Nikola-Tesla-Famous-Scientific-Illusions)
- 1919 - Electrical Experimenter - Nikola Tesla - Moon's Rotation (http://scribd.com/doc/90097922/1919-Electrical-Experimenter-Nikola-Tesla-Moon-s-Rotation)

I invite everyone who understand what is general relativity, and can analyze the motion of an object in different reference systems, and to expose the arguments for or against those supported by me.My bold. What is your definition of "real"?

I stand by my remarks in post #6. In my opinion you are giving us an example of the quibbling with words that I mentioned there. The Moon is clearly undergoing a compound motion as reckoned in a frame of reference in which the background stars are virtually stationary. I find no mathematical fault in describing this motion as a vector sum of a rotation of the Moon about its center combined with a translation of that center along an approximately elliptical orbit.

Jeff Root
2012-May-15, 05:35 AM

What distinguishes axial rotation from rotation which is
not axial?

-- Jeff, in Minneapolis

2012-May-15, 06:54 AM
@Jens
The bicycle wheel will rotate in both cases, in your hand and going on the ground. In both cases we can say that it has its own axial rotation. But I think it is not the same case as with the Moon.

@Timmy
Yes, I totally agree! It rotates and has its OWN angular momentum (i wrote with caps look font because we know that there can be two kind of angular momentum; rotating/spin angular momentum and revolution/orbital angular momentum, or with other words, rotating/spin angular momentum is permanently wrt an external - to its own physical body - point of reference, and revolution/orbital angular momentum could be wrt to an external - to the circle/elliptic of revolution/orbiting - point of reference or wrt to the center of rotation/spin/symmetry/gravity/mass...depending on each case in part).

@Hornblower
I read your post no.6, and I agree with you, the Moon continuously changes the direction it is facing with respect to the fixed stars as it goes around its orbit. But fixed stars represent an external (see the above explanations) point of reference to the cirecle of revolution of the Moon. And now, because in the case of any object orbiting around a something else, there will always exists two point of references, one internal and other external to the circle/ellipse of revolution, tell me please how you see the Moon angular momentum wrt to the any internal point of reference (more easier wrt to the center of rotation)

@Jeff Root
Own axial rotation, is a term that I use instead of spin rotation, because someone caught my attention that the spin is used only at the quantum level. But of course, we can agree, here on this forum, to use spin rotation. I do not mind the conventions and the words used. I only care to understand how things are with our Moon. It is as I say, or I have gone crazy?

Jens
2012-May-16, 12:14 AM
@Jens
The bicycle wheel will rotate in both cases, in your hand and going on the ground. In both cases we can say that it has its own axial rotation. But I think it is not the same case as with the Moon.

In a sense, it is the same case though. Suppose that we look at the moon from a vantage point on the sun. What would we see? I think basically what you would see is this: you would see the moon going forward in one direction, though it would isolate nearer and closer to you, and the speed would get faster and slower at times. And you would see it slowly rotating so that you would see all its faces from time to time.

Jens
2012-May-16, 12:16 AM
And now, because in the case of any object orbiting around a something else, there will always exists two point of references, one internal and other external to the circle/ellipse of revolution, tell me please how you see the Moon angular momentum wrt to the any internal point of reference (more easier wrt to the center of rotation)

I know this question wasn't addressed to me, but sort of as a follow-up, because you mentioned the fixed stars. How about a Foucault pendulum. Do you think it would work on the moon?

John Mendenhall
2012-May-16, 02:12 AM
I know this question wasn't addressed to me, but sort of as a follow-up, because you mentioned the fixed stars. How about a Foucault pendulum. Do you think it would work on the moon?

What a great idea! If we build a polar colony on the Moon, also build a huge Foucault pendulum on the pole! Line the swinging up with the direction to the Sun. It will make a revolution every 28 days, that's 56 little chess pieces in a circle around the low point of the swing to knock over at 2 per day. The colonists will waste more time watching the pendulum swing sooo slowly at 1/6 g than we waste playing solitaire on Windows.

P Timmy
2012-May-16, 04:05 AM
In the animation below... do you agree that the object in the center is rotating on an internal axis and has angular momentum?

Yes, I totally agree! It rotates and has its OWN angular momentum

The objects in the animation are interchangeable. The object in the center is rotating while in a stationary position... and the other object is rotating while revolving around the center object. You agree that the object in the center is rotating and has angular momentum... so why would the object in the center not have that angular momentum just because it was in orbit?

http://www.bautforum.com/attachment.php?attachmentid=16614&d=1332902697

2012-May-16, 09:13 AM
@Jens
Yes, you are right. We, from Sun or from any other point of reference external to circle/ellipse of revolution/orbit of the Moon around the Earth, will see all faces of the Moon on the duration of a complete revolution. But this happens due to the Moon consecutive placement on the revolution/orbit path around the Earth, not due to the Moon's spin rotation.

Let's make a short analysis of the cases when we can not see all faces of an object that revolve:
1 - from a external, fixed or moving point of view (internal to the circle/ellipse of rotation - any other kind of movement except the rotation motion with the same revolution/orbital angular speed, around the same center of rotation like of the object revolving):
a - when the object is revolving around a center of rotation/symmetry/mass and has no spin rotation - false
b - when the object is revolving around a center of rotation/symmetry/mass and has spin rotation - false

2 - from an internal, fixed or moving point of view (internal to the circle/ellipse of rotation)
a - when the object is revolving around a center of rotation/symmetry/mass and has no spin rotation - true
b - when the object is revolving around a center of rotation/symmetry/mass and has spin rotation - false

From this short analysis we can see the single point of view from which we con not see all faces of the object is point "a" from second case, namely, "when the object is revolving around a center of rotation/symmetry/mass and has no spin rotation". Do you consider that there is something wrong in my reasoning? If yes, please argue here!

In connection with the Foucault's pendulum, because I consider that the Moon has no spin rotation, I suppose it will not working in proper manner. It will not work!

@John Mendenhall
Great and nice imagination! I like your description. And of course, your triky suggestion! Even I am not sure if Foucault pendulum is a right instrument to indicate the Earth spin rotation (Decrypting the Eclipse - A Solar Eclipse, Global Measurements and a Mystery (http://science.nasa.gov/science-news/science-at-nasa/1999/ast06aug99_1/)), let's make a short analysis about the movement of the Foucault pendulum in two cases when it is on the Moon's pole:
1. - wrt the Sun
If the pendulum will start swinging lined up with the Sun, after 24 hours, when the Moon will move on the orbit with a specific distance from the initial point of start, the pendulum will indicate on the same initial direction, will swing following permanently the same path, that means it will have a 0 degree deviation to the initial point of swinging. Not imagine that the pendulum will permanently follow the relatively fixed position of the Sun, and will divide the Moon into 56 slices. In conclusion, the pendulum will maintain the same direction of swinging wrt the Moon, but will apparently change its direction of swinging wrt to the Sun, due to Moon's orbital motion. So, after 7, 14, 21 and 28 days the pendulum will swing on the same direction wrt the Moon, but its swinging line will make a 90, 180, 270 and 360 degrees wrt the Sun.
2. - wrt the Earth
If the pendulum will start swinging lined up with the Earth, after 24 hours, when the Moon will move on the orbit with a specific distance from the initial point of start, the pendulum will indicate on the same initial direction, will swing following permanently the same path, that means it will have a 0 degree deviation to the initial point of swinging. Not imagine that the pendulum will permanently follow the relatively fixed position of the Earth, and will divide the Moon into 56 slices. In conclusion, the pendulum will maintain the same direction of swinging wrt the Moon, and will not change its direction of swinging wrt to the Earth, on its orbital motion. So, after 7, 14, 21 and 28 days the pendulum will swing on the same direction wrt the Moon, and will maintain the same 0 degree for the swinging line wrt the Earth.

@Timmy
That two objects are interchangeable just like objects, not like their own separate movements. Let's take the example of a bicycle wheel:

If the wheel rotate, the flag on this wheel, will make a 360 degree rotation around the central axis of rotation of the wheel, not around its own axis of rotation/spin. This is the case in your animation. You can say about that flag that it has a 360 degree rotation around its own axis, over a period of a complete rotation of the wheel? I think you can't!

1. If you translate the central object to a distance at least twice at its own diameter, you wiil transform the spinning object in a revolving object, which will revolve around the central point of origin/rotation/symmetry, transforming its spin rotation in consecutive placement of the object on the curved orbital path. The speed of revolving will be in a certain report with the initial spin motion.
2. If you translate the orbiting object to its center of revolution/orbit/rotation, will transform the revolving object in a spinning object, having a spinning speed in a certain report with the initial revolving speed.

I am not sure if this is an correct explanation, because, after all this analysis of rotational motion from different points of reference, my brain is already spinning, along with all my ideas!

Centaur
2012-May-16, 08:41 PM
So, in the Earth-Moon system, I clearly sustain that the Moon does not have its own axial rotation movement. I also sustain, that outside of the same Earth-Moon system, the Moon has ONLY an APPARENT, not a REAL own axial rotation movement.

Welcome to the discussion group, sadang.

The Moon is rotating about its axis. The Earth is rotating about its axis. Both the Earth and Moon are revolving around their common barycenter. The Earth-Moon barycenter revolves around the Sun.

As an astronaut remaining on the surface of the Moon, you would see the Sun and stars rise, traverse the sky, and set. Only the Earth would appear to remain near the same spot in your lunar horizontal coordinate system for the sky. There is a slight bulge at the lunar equator relative to its rotational axis. This implies a true inertial rotation about its axis.

P Timmy
2012-May-16, 08:52 PM
@Timmy
That two objects are interchangeable just like objects, not like their own separate movements.

Imagine a "top" (a child's toy... gif below) spinning. Sometimes these toys spin while in a stationary position... and sometimes they move in a straight line or a circle while they continue to spin. I think you agree that the toy has angular momentum while spinning in a stationary position... but what if the toy begins to move in a circle as it continues to spin... wouldn't it still have angular momentum?

http://www.bautforum.com/attachment.php?attachmentid=16887&d=1337171693

Jens
2012-May-17, 01:56 AM
@Jens
Yes, you are right. We, from Sun or from any other point of reference external to circle/ellipse of revolution/orbit of the Moon around the Earth, will see all faces of the Moon on the duration of a complete revolution. But this happens due to the Moon consecutive placement on the revolution/orbit path around the Earth, not due to the Moon's spin rotation.

What if the moon was orbiting around the earth, but was moving in such a way that if you looked from the sun, you would always see the same face of the moon? (In this case, an observer on earth would see the moon rotate once every 30 days). In that case, would you say the moon is rotating?

grapes
2012-May-17, 10:05 AM
- 1919 - Electrical Experimenter - Nikola Tesla - Famous Scientific Illusions (http://scribd.com/doc/90144454/1919-Electrical-Experimenter-Nikola-Tesla-Famous-Scientific-Illusions)
- 1919 - Electrical Experimenter - Nikola Tesla - Moon's Rotation (http://scribd.com/doc/90097922/1919-Electrical-Experimenter-Nikola-Tesla-Moon-s-Rotation)
Thanks for the links to articles by one of my favorite scientists! They are archetypically teslian!

In the next to last paragraph of the second article he says:
As I have shown before, a ball flying off will rotate at the rate of the wheel and in the same direction.
So he's actually done the experiment, but he still denies it! How unbelievably quirky!

He even allows that a Foucault pendulum on the moon would show rotation. And still denies that the moon possesses rotational momentum. Weird.

2012-May-17, 12:08 PM
@Centaur
Thanks for wishes!

I would have liked to be an astronaut .... but ... maybe next time! As an astronaut left on the Moon, I will see, indeed, stars spinning around me over a period of ~28 days, and the Earth remaining permanently near the same spot, but this is due to movement of revolution of the Moon, not because its spin motion.

In connection with its slight bulge at the Moon equator, this small difference of about 2Km between equatorial and polar radius, I think it is not a result of an axial rotation (centrifugal force or/and tidal bulge). And if we consider the real center of mass, displaced with about 1,8Km towards the Earth, and also that the higher bulge is on the far side of the Moon, I think the true inertial rotation about its own axis, became a really strange argument. Bellow is an image with a cross section of the Moon:

http://ase.tufts.edu/cosmos/pictures/Explore_figs_8/Chapter5/Fig%205_22copy.jpg

- Lunar Reconnaissance Orbiter Camera (http://wms.lroc.asu.edu/lroc/global_product/color_shaded_relief_grid)

@Timmy
In the case of a top toy, it will have initially a high speed spin rotation (a great angular speed), when it is in a stationary position, and after a while, when it start to move in circles, it will have both, revolving angular speed, and a spin angular momentum. But this toy rotation, is not similar to the Moon's rotation, because we can see all faces of this toy, when it rotate in a stationary position, and also, when it move in circles, even if we look at it form the internal circle of rotation or from its external circle of revolution.

I do not want to upset anyone, but I consider naturally, ad of common sense, that an object has its own axial rotation movement only when it actually rotates, whether static or in motion of revolution or rotating around something physical, or just around a simple rotation center. This means that me, located within the circle of rotation can see all faces of that object orbiting around me, over a period of time longer or shorter, directly related to its own angular momentum speed.

@Jens
Yes, in this case the Moon will rotate wrt any point of reference internal to its circle/ellipse of orbit/revolution, but will not rotate wrt the Sun, or any other point of reference external to the same circle/ellipse of orbit/revolution.It is a weird result, but this is the reality. Try yourself, with three apples and make with them the Moon, Earth and Sun:
1 - rotate the Moon around the Earth with a fixed face towards the Earth, and will observe the Moon will rotate wrt the Sun (will show all faces to the Sun).
2 - rotate the Moon around the earth with a fixed face towards the Sun and will see that the Moon will rotate wrt the Earth (will show all faces to the Earth).

@grapes
I like to see that you are the first who indeed read the articles of Tesla. I appreciate this, because I give more credit to Tesla than to the actual science. But, of course, this is just my point of view, and should be considered only in this form. I am a guy with an open mind, without preconceptions or dogma, and who analyze a phenomenon on all sides, from all points of view.

This statement of Tesla, noticed by you

As I have shown before, a ball flying off will rotate at the rate of the wheel and in the same direction.
have to be corroborated together with this one

There is no true analogy to these in the motion of the moon. If the gravitational string, as it were, would snap, the satellite would go off in a tangent without the slightest swerving or rotation, for there is no moment about the axis and, consequently, no tendency whatever to spinning motion.

Related to what Tesla said about Foucault pendulum...

Even the wellknown experiment with the Foucault pendulum, altho exhibiting similar phenomena as on our globe, would merely demonstrate a motion of the satellite about some axis. The view I have advanced is NOT BASED ON A THEORY but on facts demonstrable by experiment. It is not a matter of definition as some would have it. A MASS REVOLVING ON ITS AXIS MUST BE POSEST OF MOMENTUM. If it has none, there is no axial rotation, all appearances to the contrary notwithstanding.

I am not sure at what phenomena he make references in his assertion that "... altho exhibiting similar phenomena as on our globe...", but what is clear for me is what he say next, namely, "[i]... would merely demonstrate a motion of the satellite about some axis...". From this phrase is evident that he referes to some other axis of rotation, like that of revolution around the Earth, or around the Sun, or around the galactic center, or... any other kind of exis of rotation, not only to the Moon's axial spinning axis.

At least, this is what I undestand from those written by Tesla. If you understand other way, and consider that I am wrong in my understandings, please post here your point of view and will try togheter, or with help from others, to find the real sense of what Tesla claim in his articles.

grapes
2012-May-17, 03:34 PM
At least, this is what I undestand from those written by Tesla. If you understand other way, and consider that I am wrong in my understandings, please post here your point of view and will try togheter, or with help from others, to find the real sense of what Tesla claim in his articles.
Clearly, Tesla knew what to do, and how to do it. And, unlike most, he actually did it, apparently. He just couldn't reconcile it in his head. Truly, a beautifully crazy person.

P Timmy
2012-May-18, 03:03 AM
In the case of a top toy, it will have initially a high speed spin rotation (a great angular speed), when it is in a stationary position, and after a while, when it start to move in circles, it will have both, revolving angular speed, and a spin angular momentum.

Yes... the top has rotational momentum whether its rotating in a stationary position or rotating while moving in a circle.
And whether stationary or moving in a circle... the top would have rotational momentum even if it was rotating only once every 27.3 days.

The objects below are spinning tops and both are spinning one time every 27.3 days... don't you agree that both have rotational momentum?

http://www.bautforum.com/attachment.php?attachmentid=16614&d=1332902697

Centaur
2012-May-18, 03:37 AM
As an astronaut left on the Moon, I will see, indeed, stars spinning around me over a period of ~28 days, and the Earth remaining permanently near the same spot, but this is due to movement of revolution of the Moon, not because its spin motion.

Please read my post #25 in this thread. If you were located far north of the solar system yet were blind to the Earth, you would see the Moon revolving around the Sun in a continuously concave orbit, unlike all other planetary satellites. At the same time you would see the Moon rotating on its axis. Simply because the Moon's originally shorter rotation period eventually increased to 27.32 days, does not mean the rotation stopped. I would be dumbfounded if a Foucault pendulum could not prove this. If you agree this is all so, yet still want to claim the Moon is not rotating, then we are dealing with semantics and you are out on a limb by yourself.

P Timmy
2012-May-18, 04:29 AM
According to you... the doll in the center makes two real rotations during the time it takes the doll in orbit to make a complete revolution... and the doll in orbit rotates two times per revolution but only one of those rotations is real and the other rotation is only apparent.

As to the doll in orbit... which of its rotations is real... the first one it makes... or the second one it makes?

http://www.bautforum.com/attachment.php?attachmentid=16895&d=1337313048

2012-May-18, 09:35 AM
@Timmy
1'st post - I don't agree. The central top indeed, have angular momentum, but the revolving top don't have any angular momentum. The revolving top is like a top that revolve in a circle without having spinning speed. An impossibility!

2'nd post - In second animation, you exposed correctly the rotation of both dolls. Let's make the analysis of each one doll separately:
1. - central doll
1.a - from any external POV
- make two real axial rotations over e period of complete revolution of the orbiting doll. That means we can see two real rotation around its own axis, from any external point of reference, from anywhere in the universe.
1.b - from any internal POV
- nor applicable

2. - orbiting doll
2.a - from any external POV
- it will make two rotations around its own axis over a complete revolution time.
2.b - from any internal POV
- it will make a single rotation around its own axis over a complete revolution time.

... and the doll in orbit rotates two times per revolution but only one of those rotations is real and the other rotation is only apparent...
I see that you consider the movement of the orbiting doll only from external point of view (external to the circle of revolution). Maybe I am wrong, but this is what I understand from your phrase

But now, make an exercise of imagination, and look at the movement of the orbiting doll, from any internal point of view (internal to the circle of revolution). From this poin you will see only a single rotation around its own axis of the orbiting doll over a complete revolving movement. Look closely, and tell me if I am right or wrong?

And to answer to your question, I can only say that I don't know which answer is the correct one: two axial rotations seen from any external POV or one axial rotation seen from any internal POV! This is the big question! Why is this difference, if my reasoning is correct? Or maybe is not right and if you notice where I'm wrong, please show me!

@Centaur
I do not want, to get me wrong. From articles of Tesla and in what I read on the net and from my personal library, I do not clear at all, why the science says the Moon own axial rotation is synchronous with that of the revolution, when it seems to me obvious that the Moon does not rotate around its own axis.

On the other hand, I'm not trying to convince anyone of anything, but, I am trying to explain myself, this dichotomy, which represents the existence or not of the Moon's own axial rotation, analyzed from two points of view, internal and external of the circle of revolution.

Returning to you last message, I would not want to debate in this topic the rotation of the Moon around the Sun, because I did it on another forum, and we will contradict more, and will dilute the actual theme of topic. My short answer is: I don't agree with the Moon rotation around the Sun. Let's resume only at the Moon's axial rotation!

"Simply because the Moon's originally shorter rotation period eventually increased to 27.32 days, does not mean the rotation stopped" it is only a working hypothesis, and not a relative or absolute truth!. Neither Newton nor anyone else ever since can not say with certainty how the Moon formed, or who initially gave the impulse for the rotation of celestial bodies. This represents just one of many absolutes hypothetical work, expressed in Newton's axioms expressed in "Philosophiæ Naturalis Principia Mathematica", and which is based the whole his gravitational theory.

Also, to this rhetorical interrogation,
"...does not mean the rotation stopped. I would be dumbfounded if a Foucault pendulum could not prove this..." I can not answer, other than with another rhetorical interrogation statement: "I would be dumbfounded if a Foucault pendulum could prove this!".

grapes
2012-May-18, 01:23 PM
I can not answer, other than with another rhetorical interrogation statement: "I would be dumbfounded if a Foucault pendulum could prove this!"
Actually, I think Tesla concedes that a Foucault pendulum on the moon would show rotation. Tesla's error is in not breaking down the math far enough--not one of his strong points.

I'll see if I can find the quote in that paper.

ETA: OK, second paper, second page, first few lines:

Even the well-known experiment with the Foucault pendulum, altho exhibiting similar phenomenon as on our globe, would merely demonstrate motion of the satellite about some axis.

Centaur
2012-May-18, 03:27 PM
...when it seems to me obvious that the Moon does not rotate around its own axis.

The Moon's rotation rate is virtually constant as though it were clockwork. It's angular speed of revolution relative to the Earth varies due to the eccentricity of its orbit. This causes the Earth not to appear at a fixed location in the lunar sky, but produces an apparent monthly oscillation. Earthbound observers see this as a libration of the Moon's surface. Due to the interaction of Earth's orbit around the Sun and the Moon's orbit around the Earth, as viewed from Earth the Moon does not align itself with a particular star in exactly the same period of time from month to month. But a particular star crosses a lunar observers meridian every 27.321662 days precisely. Therefore the Moon's rotation rate and revolution rate are not constantly in perfect sync. It is only after a long period of time that the rates average to the same value. The Moon has an inertial rotation about its axis. I can't imagine why you so adamantly want to dispute this.

Swift
2012-May-18, 04:49 PM
And to answer to your question, I can only say that I don't know which answer is the correct one: two axial rotations seen from any external POV or one axial rotation seen from any internal POV! This is the big question! Why is this difference, if my reasoning is correct? Or maybe is not right and if you notice where I'm wrong, please show me!

Let me make this VERY clear. As long as you really are "just asking", so as to understand the mainstream physics, then this conversation may continue. But you may not cross the line into advocating a non-mainstream idea (such as the moon doesn't rotate); that may ONLY be done in the ATM forum. Consider that an official warning. If you violate this, you will be infracted.

2012-May-18, 09:14 PM
@grapes
I already answered to your last message, in my previous message. I will insert here, using quotes the entire explanations given there. here it is:
Related to what Tesla said about Foucault pendulum...

Even the wellknown experiment with the Foucault pendulum, altho exhibiting similar phenomena as on our globe, would merely demonstrate a motion of the satellite about some axis. The view I have advanced is NOT BASED ON A THEORY but on facts demonstrable by experiment. It is not a matter of definition as some would have it. A MASS REVOLVING ON ITS AXIS MUST BE POSEST OF MOMENTUM. If it has none, there is no axial rotation, all appearances to the contrary notwithstanding.
I am not sure at what phenomena he make references in his assertion that "... altho exhibiting similar phenomena as on our globe...", but what is clear for me is what he say next, namely, "... would merely demonstrate a motion of the satellite about some axis...". From this phrase is evident that he referes to some other axis of rotation, like that of revolution around the Earth, or around the Sun, or around the galactic center, or... any other kind of exis of rotation, not only to the Moon's axial spinning axis.

At least, this is what I understand from those written by Tesla. If you understand other way, and consider that I am wrong in my understandings, please post here your point of view and will try together, or with help from others, to find the real sense of what Tesla claim in his articles.

@Centaur
The synchronicity to which I referred in the previous message, is described on wikipedia, that is, ...The Moon is in synchronous rotation: it rotates about its axis in about the same time it takes to orbit the Earth. (http://en.wikipedia.org/wiki/Moon). And your explanation is more accurate, I understand it, I appreciate it, I agree with it, and thank you for it.

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.

You ask why I want to dispute the Moon's axial rotation! Is very simple, because I don't want to accept something that I don't understand. And that is why I'm here, to understand. But not superficially, but to really understand, as deeper as is possible, the reality and the existence of its own axial rotation movements of the Moon.

@Swift
I really don't understand your intervention! What I did wrong? Or I have to ask, and accept any explanations as it is? Exactly like a robot! If I don't understand something, I consider natural to ask explanations, and to express my opinion, because of this I have a head over the shoulders and a brain in it.

And what is an ATM forum?

Anyway, I consider your behavior, as one of intimidation, or censorship or free speech and think. And if you really think I did something wrong, you can close my account or delete my posts, or just tell me not to post, and is enough!

grapes
2012-May-19, 02:33 AM
@grapes
I was surprised when I first read that article to find Tesla agreeing with most of the objections to the argument. In other words, when people usually deny that the moon rotates, they also deny that a ball loosed from a whirling string would continue rotating, or they deny that a Foucault pendulum on the moon would show the rotation--but Tesla was too smart for that. He actually did the experiments. However, he was led astray by a simple error in math, one that any freshman engineer (OK, an engineer who has finished freshman year) would know to avoid.

Tesla forgot to apply the parallel axis theorem. Stupid mistake.

ETA: Speaking of stupid mistakes, I re-read that part of the paper and now I'm thinking that Tesla denies the parallel axis theorem, that it doesn't agree with his experiments! This is even more interesting. But, sorry about that.

2012-May-19, 06:51 AM
@grapes
Tesla indeed, made the experiments weight whirled on a string or in a sling.. He studied the results and he concluded that it is not the same case as is for the Moon, as he stated in the second article:
"There is no true analogy to these in the motion of the moon. If the gravitational string, as it were, would snap, the satellite would go off in a tangent without the slightest swerving or rotation, for there is no moment about the axis and, consequently, no tendency whatever to spinning motion."

In this statement of Tesla, I underlined that phrases that I consider essential.
- There is no true analogy to these in the motion of the moon - from this phrase he clearly disagree with the Moon's own axial rotation
- gravitational string - using this phrase he clearly differentiate this kind of string apart from the above mentioned whirling string or sling.
- for there is no moment about the axis - again he clearly maintain the assertion that the Moon has no own axial rotation motion.

Conclusion - He consider the case of the Moon linked to Earth by "the gravitational string" a separate and totally different case, apart from a weight whirled by a string or a sling. He don't agree with these two often used analogies.

Related to Foucault pendulum experiments, I repeat again what he wrote in his article: "... Even the wellknown experiment with the Foucault pendulum, altho exhibiting similar phenomena as on our globe, would merely demonstrate a motion of the satellite about some axis...". I also underlined the phrases that I consider relevant from his statement.
Let's see:
- altho exhibiting similar phenomena as on our globe - means it will display phenomena similar to those on Earth, not identical.
- about some axis - means about some axis, any different external axis of rotation, not strictly about its center of mass, or it own rotational axis, or its center of symmetry, or its center of gravity.... For an object can exists an infinity of axis of rotation, even internal or external to its physical body limits.

As we know for sure, a Foucault pendulum can only show the rotational movement of a physical body on it is placed, wrt an external point of reference. Always, wrt to an external point of reference. If the rotational motion does not exists, there will be just a swinging movement of the pendulum. As is the case of the Moon. This is what he finely is trying to suggests in that phrase. At least in my opinion!

Conclusion - He did not consider the Moon to exhibits identical phenomena like on the Earth, but instead, he consider that the pendulum will exhibit no own axial rotation of the Moon.

Now, related to the theorem of parallel axis, that you consider he missed in his analysis of Moon's rotation. This theorem has availability when the analyzed object has a really axis of rotation, and conclusively it really has an axial rotation. But, as we can see from his article's mathematical and experimental demonstrations, he proved that the Moon has no axial rotation, at all. The Moon has indeed, an axis of rotation, but this axis is external to its physical body, and is the axis of revolution/orbiting. This is the single axis of the Moon. And yes, now we can apply the theorem of two parallel axis, and can calculate the Iz.

And do not forget an essential thing, any inertial momentum calculation is done in relation to something else, not with himself. In relation with other reference. In this specific case, we try to calculate the inertial moment of the new axis, parallel to first, starting this calculation from the premise that the first axis (Ix) has a real inertial moment. Wrong premises, wrong results!

Conclusion: He did not apply the theorem of two parallel axis, because he did not consider it valid in the case of the Moon, not because he did not know it, or because it doesn't agree with his experiments!

This is just my point of view, not an absolute truth. My arguments are not necessarily against those exposed by you, but my arguments just come to complete your arguments, according to what and how I understand what was written by Tesla.

captain swoop
2012-May-19, 08:39 AM
@grapes
@Swift
I really don't understand your intervention! What I did wrong? Or I have to ask, and accept any explanations as it is? Exactly like a robot! If I don't understand something, I consider natural to ask explanations, and to express my opinion, because of this I have a head over the shoulders and a brain in it.

And what is an ATM forum?

Anyway, I consider your behavior, as one of intimidation, or censorship or free speech and think. And if you really think I did something wrong, you can close my account or delete my posts, or just tell me not to post, and is enough!

Read the rules for posting to the Forum, they are linked at the bottom of this post. Asking questions is OK as long as that is all you are doing. IF you get mainstream answers to a question but then dispute them and advocate your own, or someone elses ideas that are against the mainstream of science it must be done in the ATM Forum. Please take some time to read the rules for posting to the board, they are linked at the bottom of this post.
Please do not argue or dispute Moderator actions ina thread, it is disruptive, if you have a disagreement then use the reporting triangle at the bottom left corner of the post and report it to the moderation team.

Nobody is censoring you or disputing your 'free speech' the Internet is full of places for you to advocate any idea you want. On this board there are certain rules that go with this advocacy and certain places that it is allowed.

Thank you

2012-May-19, 10:40 AM
@captain swoop
Thank you very much for this clear explanations. I read the forum rules and I consider that are very restrictive. Just seems to be a forum that respects free speech and thinking, in reality is censored any deviation from the current scientific rules. Just like in the joke with monkeys and bananas that can be read here: Monkeys and bananas! (http://cpdtraining.blogspot.com/2006/11/gorillas-and-bananas.html). I ask all those reading this post to ask himself: With which monkey, I can identify? And the fundamental question, why ? I am really disappointed to still see this kind of behavior in the actual stage of e(in)volution of humanity. Really disappointed!

So, my decision is to stop posting here, on this topic and also on this forum, because in my analysis of the Moon's movements, I will have to go to the basis of gravitational theory, to the premises on which it was based, to all those Newton's axiomatic defined absolutes described in his Principia, and in this case I can not understand how someone could take the decision of what is right or wrong.

@All
Sorry for my intervention inopportune, and for daring to put all those uncomfortable questions, but if I have caused as little curiosity, always look for answers by yourself, always beyond appearances, even if for that you have to turn the world upside down! Thank you for supporting me and success on the road of knowledge.

grapes
2012-May-19, 11:13 AM
- altho exhibiting similar phenomena as on our globe - means it will display phenomena similar to those on Earth, not identical.
Of course it won't be identical, the moon rotates once per month, the earth once per day.

Conclusion - He did not consider the Moon to exhibits identical phenomena like on the Earth, but instead, he consider that the pendulum will exhibit no own axial rotation of the Moon.
No he said it would exhibit similar behavior--in referring to it aligning with outside references.

Conclusion: He did not apply the theorem of two parallel axis, because he did not consider it valid in the case of the Moon, not because he did not know it, or because it doesn't agree with his experiments!
He says it's not appropriate for the moon because it's not appropriate for the experiments!

The whole article depends upon a simple experiment that is done in a freshman lab! This is incredible! How in the world did he screw that up?

Jeff Root
2012-May-19, 04:39 PM

I think it is too bad that you choose to run away when
want to convince other people that your goofy ideas
about rotation are right, but you aren't willing to do
the work required to convince anyone. All you end up
doing is demonstrate that, like Tesla, your knowledge
each other.

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

P Timmy
2012-May-19, 06:08 PM
@captain swoop
Thank you very much for this clear explanations.

Yes... thank you for the clear and respectful explanation... and below is a link to advice for posting at ATM.

Even though I read the rules before posting here... it now appears that I should have started this thread in the ATM area (link below)...

http://www.bautforum.com/forumdisplay.php/17-Against-the-Mainstream

and then there wouldn't have been any need to warn Sadang about infractions if he did break a rule in this thread. So I apologize for my part that lead up to Sadang choosing to leave. But how about moving this thread to ATM and maybe Sadang would come back... and those that choose to could continue on with what has been a very respectful thread with potential to come to a meeting of the minds?

R.A.F.
2012-May-19, 06:56 PM
...it now appears that I should have started this thread in the ATM area...

Not at all. You were not advocating an ATM idea.

Since he finds the rules here, "restrictive", I doubt he would.

Centaur
2012-May-19, 07:40 PM
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.

P Timmy
2012-May-22, 12:32 PM
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 :)

Hornblower
2012-May-23, 06:51 PM
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.

R.A.F.
2012-May-23, 08:00 PM
...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.

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.

P Timmy
2012-May-23, 11:24 PM
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.

gkell1
2012-Jun-16, 08:20 PM

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.

Hetman
2012-Jun-27, 01:52 PM
total angular momentum of the body in the synchronous rotation:
L = I_e W + I_o w = I_e W, where: w - spin
Thus the spin of the body is probably zero.

grapes
2012-Jun-27, 05:28 PM
total angular momentum of the body in the synchronous rotation:
L = I_e W + I_o w = I_e W, 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.

Hetman
2012-Jun-28, 12:16 AM
Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

E = E_w + E_s
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.

Hornblower
2012-Jun-28, 01:15 AM
Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

E = E_w + E_s
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?

Hetman
2012-Jun-28, 01:36 AM
Maybe it is spinning ... with minimum energy.

grapes
2012-Jun-28, 03:18 AM
Spin seems to be zero, which means a minimum of energy, and that is why such synchronization is preferred.

E = E_w + E_s
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.

Jeff Root
2012-Jun-28, 07:33 AM
The moon is spinning on its own axis, that's irrefutable.
Do they convey additional information? If so, what
information?

-- Jeff, in Minneapolis

grapes
2012-Jun-29, 10:30 AM
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.

Jeff Root
2012-Jun-29, 05:49 PM
So maybe the question to ask is "What is an axis?"

-- Jeff, in Minneapolis

grapes
2012-Jun-29, 06:39 PM
Have we answered "what is spinning?" already? If not, let's do that one first. :)

Hetman
2012-Jun-29, 09:07 PM
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. :rolleyes:

pzkpfw
2012-Jun-29, 09:55 PM
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?)

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.)

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. :rolleyes:

So if a bowling ball rolls down the lane, where do you claim the axis of rotation is?

Hetman
2012-Jun-29, 11:26 PM
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.

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.

pzkpfw
2012-Jun-29, 11:37 PM
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?

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?

Hetman
2012-Jun-30, 12:27 AM
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.

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).

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.

pzkpfw
2012-Jun-30, 12:32 AM
... 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?

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.

PetersCreek
2012-Jun-30, 12:43 AM
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 (http://www.youtube.com/watch?v=R4Vjmhr_sbA) 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.

grapes
2012-Jun-30, 01:13 AM
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. :)

pzkpfw
2012-Jun-30, 01:24 AM
... 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.

Hetman
2012-Jun-30, 06:55 PM
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.

Hetman
2012-Jun-30, 07:54 PM
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.

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.

R.A.F.
2012-Jun-30, 08:25 PM
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...

pzkpfw
2012-Jun-30, 09:21 PM
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?

Hetman
2012-Jun-30, 11:39 PM
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.

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

R.A.F.
2012-Jul-01, 12:10 AM
Some reminiscences of the early 20th century?

This point can not escape, nor the axis break.

What the heck are you talking about???

Hetman
2012-Jul-01, 01:25 AM
I tell that a body rolling without slipping rotates around the axis at the point of support.

pzkpfw
2012-Jul-01, 03:59 AM
http://en.wikipedia.org/wiki/Instant_centre_of_rotation

Thanks.

So the words that go along with the picture you claimed supported your assertion begin (my underline):

Consider the planar movement of a circular wheel rolling without slipping on a linear road; see sketch 3. The wheel rotates around its axis M, which translates in a direction parallel to the road. The point of contact P of the wheel with road does not slip, which means the point P has zero velocity with respect to point M. Thus, at the instant the point P on the wheel comes in contact with the road it becomes an instant centre.

You've learned about the Instant centre of rotation, and are over-applying it.

grapes
2012-Jul-01, 11:17 AM
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.
I don't think they were saying the axis is vertical--instead, it was horizontal, parallel to the floor and perpendicular to the direction if motion. That leaves out of the picture all of the physics of ball english and lane grooming, but we can pick that split up later. :)

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.

Perhaps?

No, that would only happen if that effect was as strong as the inertial forces, which is far from the case.

Very good. There is no man on earth who understands physics.
That's not what I meant by that. And, re-reading it, I probably should have said "cannot" in the last statement.

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

That's the problem with both interpretations. If a ball is translating, it's internal axes are moving. It is sometimes appropriate to choose an external axis, which is not moving, for describing the rotation. One just has to be careful.

Hetman
2012-Jul-01, 02:03 PM
So the words that go along with the picture you claimed supported your assertion begin (my underline):

You've learned about the Instant centre of rotation, and are over-applying it.

What I'm over-applying?

It is clear that both axes here are equally good (from a mathematical point of view), and the problem reduces to choosing the right frame of reference.

But we still have one criterion for selection of the reference system: the simplicity of the description of the phenomenon. And here wins the axis at the point of support.

And moreover in the case of rolling on an inclined plane we obtain a direct causal relationship: clear, complete and natural explanation of the process.

I think it's really the famous half-spin: rotation in conditions of limited freedom.

Hetman
2012-Jul-01, 03:56 PM
No, that would only happen if that effect was as strong as the inertial forces, which is far from the case.

The effect is sufficiently strong for the synchronization of the Moon, so there is a reasonable suspicion that for the pendulum, it will also be sufficient.
The forces of inertia are not accidentally proportional to gravity.

In any case, the plane of oscillation does not remain there at rest relative to the stars.

grapes
2012-Jul-01, 07:40 PM
The effect is sufficiently strong for the synchronization of the Moon, so there is a reasonable suspicion that for the pendulum, it will also be sufficient.
Suspicion??

The forces of inertia are not accidentally proportional to gravity.
Exactly. So if the moon were not rotating with respect to the stars, how long do you think it would take the earth to accelerate it to one full rotation per 27 days? In order for that lunar pendulum to not show that difference, the acceleration would have to occur in much less than 27 days. I don't think that's a reasonable suspicion at all.

In any case, the plane of oscillation does not remain there at rest relative to the stars.Close enough :)

Jeff Root
2012-Jul-01, 07:59 PM
Since the rotation of a pendulum is always stopping and
starting again, I'd think it must be more susceptible than
a rotating wheel to small forces which would change the
rotation plane. How much more?

-- Jeff, in Minneapolis

grapes
2012-Jul-01, 11:04 PM
Since the rotation of a pendulum is always stopping and
starting again, I'd think it must be more susceptible than
a rotating wheel to small forces which would change the
rotation plane. How much more?
Which small force? Then maybe we can calculate that.

PetersCreek
2012-Jul-01, 11:14 PM
I don't think they were saying the axis is vertical--instead, it was horizontal, parallel to the floor and perpendicular to the direction if motion. That leaves out of the picture all of the physics of ball english and lane grooming, but we can pick that split up later. :)Perhaps?

I was only pointing out that the case of a vertical axis is the only one that coincides with the point of contact (P) with a floor plane. My example of a hooking ball was but one case that contradicts Hetman's claim.

Staying with the bowling analogy, Hetman, lane oil often leaves a visible track around the ball. In the case of a dead roller (axis parallel to the floor and perpendicular to the direction of travel) this track appears at the ball's "equator". Do you also argue that the Earth's axis is at some point P along the planet's equator?

Hetman
2012-Jul-01, 11:59 PM
So if the moon were not rotating with respect to the stars, how long do you think it would take the earth to accelerate it to one full rotation per 27 days?

I don't know. You can put the ball on the moon with zero rotation, relative to stars, and see how long it will be there spinning.

Jens
2012-Jul-02, 12:48 AM
A player running around the stadium is not spinning.

I'm intrigued by this. Why do you say the runner is not spinning? What about a person throwing a discus? Is the athlete spinning as he prepares to toss it? To me it seems obvious he is spinning, but in fact his feet are not always in the center of a circle; he moves around as he spins. So does that movement negate the spin in your mind?

Or for example, in this video (http://www.youtube.com/watch?v=0oStQg4kNMA), would you say the person is not spinning because she is moving laterally at the same time?

grapes
2012-Jul-02, 03:15 AM
I was only pointing out that the case of a vertical axis is the only one that coincides with the point of contact (P) with a floor plane.I got that impression. But it's not true--the axis that he is talking about is another possibility. He's talking about a horizontal axis perpendicular to the direction of motion, touching the floor.

I don't know. You can put the ball on the moon with zero rotation, relative to stars, and see how long it will be there spinning.A ball on a pendulum? And by zero rotation, you mean it swings in line with the stars. I expect it would be fairly still in the same line seven days later, when the moon will have moved ninety degrees.

Jeff Root
2012-Jul-02, 04:36 AM
Since the rotation of a pendulum is always stopping and
starting again, I'd think it must be more susceptible than
a rotating wheel to small forces which would change the
rotation plane. How much more?
Which small force? Then maybe we can calculate that.
time I thought "What force would it be? Something to do
with gravity. Earth's gravity. Tidal force. Wait a minute--
a pendulum on the Moon is very short compared to the
size of the Moon. It isn't going to be nearly as much
affected by tidal force from Earth as the Moon is."

That's as far as I got before my CPU shut down again.

-- Jeff, in Minneapolis

grapes
2012-Jul-02, 04:57 AM
Yes, and the tidal force by itself does not cause the rotation of a symmetric body to speed up or slow down--friction would be involved.

Jeff Root
2012-Jul-02, 05:13 AM
My *impression* certainly is that (slight) rotation of
tidal force.

-- Jeff, in Minneapolis

grapes
2012-Jul-02, 05:52 AM
Those are heavily asymmetric bodies

Jeff Root
2012-Jul-02, 08:30 AM
Wouldn't a pendulum likely be similarly asymmetric?

-- Jeff, in Minneapolis

Hetman
2012-Jul-02, 12:18 PM
Tidal force. Wait a minute--
a pendulum on the Moon is very short compared to the
size of the Moon. It isn't going to be nearly as much
affected by tidal force from Earth as the Moon is."

Look at this.

speed of rotation:
w = 2pi / T = 2pi/27.3d = 2.66e-6 1/s

the acceleration:

a_c = w^2r = 7.e-12 m/s^2;
for r = 1 m - the size of a body.

Now the tidal forces (magnitude only):

a_t = GM/d^3 * r = 4e+14 / 384400000^3 * 1 = 7e-12 m/s^2 = a_c

grapes
2012-Jul-02, 01:39 PM
That's an extremely interesting coincidence that I've discussed before.

But remember, if your pendulum is started swinging perpendicular to the earth-moon line, the r in the tidal formula is very much smaller than a meter.

Hetman
2012-Jul-02, 01:50 PM
It does not matter, because of the relationship: w^2 r = GM/d^3 r

grapes
2012-Jul-02, 03:12 PM
It does not matter, because of the relationship: w^2 r = GM/d^3 rWhat does not matter?

Hetman
2012-Jul-02, 05:31 PM
The forces are known, so you can calculate or simulate this and then everything will be clear.

w^2 = GM/d^3;

Tidal accel:
a = w^2 (2x, y) = w^2 r (2cosf,-sinf);

Torque:
r x a = w^2 r(cosf, sinf) x r(2cosf,-sinf) = -3/2 (wr)^2 sin2f

The work of this torque must be zero in every period of the pendulum, so the stable direction is probably the only one: f ~ 0 (pendulun oscillates in the direction of the line earth - moon).

grapes
2012-Jul-02, 09:43 PM
The work of this torque must be zero in every period of the pendulum, so the stable direction is probably the only one: f ~ 0 (pendulun oscillates in the direction of the line earth - moon).I'm not convinced that it is completely zero, but if it were zero as you say, the plane of oscillation would not change--which would mean it would *not* point along the earth-moon line except twice each orbit.

Wouldn't a pendulum likely be similarly asymmetric?

-- Jeff, in MinneapolisBy saying that the torque is zero, Hetman is saying that the pendulum is symmetric. The swing of a pendulum is very close to symmetric.

Hetman
2012-Jul-03, 12:22 AM
I'm not convinced that it is completely zero, but if it were zero as you say, the plane of oscillation would not change--which would mean it would *not* point along the earth-moon line except twice each orbit.

The work must be zero, otherwise the rotation would grow without limit.

It will be just a conical pendulum, with a very thin ellipse, and such after all always precesses (in proportion to the area of ​​the ellipse).

For the observer on the moon, it will still simple pendulum (zero area), meaning zero precession.

On the Earth we also observe such a rotating conical pendulums, which only here locally are simple - linear.
Nice sketch.:rofl:

grapes
2012-Jul-03, 07:01 PM
The work must be zero, otherwise the rotation would grow without limit.
No, there are obvious ways that non-zero work wouldn't have to increase the rotation without limit.

It could sum to zero, over the cycle, without being non-zero--which is what I thought you were claiming. Another possibility is that it is a minimum at a certain orientation, the stabile orientation--which I thought was being claimed by some.

Regardless, the effect is too small to cancel the pendulum stability sufficiently that it would not show that the moon was rotating relative to it.

It will be just a conical pendulum, with a very thin ellipse, and such after all always precesses (in proportion to the area of ​​the ellipse).

For the observer on the moon, it will still simple pendulum (zero area), meaning zero precession.

On the Earth we also observe such a rotating conical pendulums, which only here locally are simple - linear.
Nice sketch.:rofl:What sketch? And what's so funny about it? :)

Jens
2012-Jul-04, 02:12 AM
The work must be zero, otherwise the rotation would grow without limit.

I know you're busy answering other queries, but I really would be interested in what you think about the skater video I posed (#102).

Hetman
2012-Jul-04, 01:58 PM
Runners, horses and cars do not spin when running.

Hetman
2012-Jul-04, 02:38 PM
More interesting problem is a gyroscope on the moon.

In the case of Earth, there is probably some synchronization here:

The radius of the orbit / radius of the Earth * cosi:

d / Rcosi = 150 mln / 6370.cos23.4 = 25 600
probably the period of precession, by the orbital period Tp / T.

Moreover, now the axial tilt probably decreases, and precession speeds up, which agrees with this dependency.

Jeff Root
2012-Jul-04, 11:05 PM
Hetman,

17225
Hammer 1

Do you agree that the geologist's hammer in this
movie clip is rotating?

-- Jeff, in Minneapolis

Hetman
2012-Jul-05, 12:05 AM
You want to convince me?
Color blind will not convince the normal sighted person that everything is gray.

R.A.F.
2012-Jul-05, 12:27 AM
you want to convince me?

Although I can not compel you to provide evidence for your "idea", it is You who is making the extrordinary claim, so it is your "job" to convince us.

Color blind will not convince the normal sighted person that everything is gray.

Empty platitudes are not evidence.

Swift
2012-Jul-05, 12:47 AM
You want to convince me?
Color blind will not convince the normal sighted person that everything is gray.
Hetman,

Lose the attitude

Hetman
2012-Jul-05, 12:43 PM
Although I can not compel you to provide evidence for your "idea", it is You who is making the extrordinary claim, so it is your "job" to convince us.

Empty platitudes are not evidence.

I can give you many examples of truly extraordinary claims.
For example, contraction of bodies in motion.

The effect was formally justified by finding that it can not be observed in practice, because it is non-observable at all.

tusenfem
2012-Jul-05, 08:26 PM
I can give you many examples of truly extraordinary claims.
For example, contraction of bodies in motion.

The effect was formally justified by finding that it can not be observed in practice, because it is non-observable at all.

Stick to the topic, and don't come up with any claims that suit your ATM views but have nothing to do with the topic.
This earns you an infraction.

R.A.F.
2012-Jul-24, 06:02 PM
I can give you many examples of truly extraordinary claims.
For example, contraction of bodies in motion.

This might seem to be an extraordinary claim on it's "face", but mainstream science understands why bodies in motion, "contract", so it isn't all that "extraordinary".

Anything else?...

tusenfem
2012-Jul-25, 06:38 AM
This might seem to be an extraordinary claim on it's "face", but mainstream science understands why bodies in motion, "contract", so it isn't all that "extraordinary".

Anything else?...

When I tell Hetman not to come with these kind of off-topic ATM claims, then that also means that you should not comment on them either, "feeding a discussion."
You should know better than that, specially because my warning is right between Hetman's message and your comment.
Infraction.

R.A.F.
2012-Jul-25, 04:02 PM
I'm sorry...was just wondering if hetman was participating further in this thread...apparently not...