Why Is The Moon Not Spinning Then?

That is correct if you want to FALSELY assume that the total angular momentum of the moon is only its orbit about the baracenter (common center of mass) but not a very reasonable POV because it ignores the fact that the moon is actually orbiting the sun, not the Earth or their common center of mass.

If the Earth were to explode and scatter into a zillion different widely separated pieces, the orbit of the moon about the sun would only very slightly change (not have the tiny "wobble" it current does)*. The moon would continue to spin about its own axis ~13 full rotation in the ~365 day trip around the sun.

This is the same point cluelusshusbund has been making with his "released tennis ball" continuing to spin around its axis. Your POV is a very provincial Earth based one. If you lived on Mars you would see the Earth as spinning on its own axis ~365 times and the moon spinning on its own axis ~13 times each Earth (or moon) year.

As I tried to get you to understand in prior post all you need to do to see how strange and provincial your POV is, is to imagine the earth spin slowing. Take it in "baby steps" if you need to: down to a 100 spin rotations/per year, Then only 50 rotations / year, then only ~13 rotations /years (now with the same face always turned to the moon and a bridge built between them)

I again ask why is O spinning but o is not? (Referring to my prior post with the "typed drawings.")
You are totally inconsistent to claim one is spinning about its own axis and the other is not just because their spin rates different in magnitude.

Consider an even slower spinning Earth, say 10 rotations / year. Then the moon is spinning faster than the Earth is about its own axis.

The Earth could continuously lower its spin rate - Do you say that at 14 rotations/ per year it is spinning about it own axis but at ~13 / year it is not?

What principle are you using to make this arbitrary cut off? Do you not realize that at 10 rotations / year the moon is spinning about its own axis faster than the Earth is?

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* Express the Earth moon separation in Astronomical units (AU). You will see that adding that tiny fraction of an AU to 1.0 (when moon is most distance from the sun) and subtracting it from 1.0 (when the moon is closest to the sun) makes a "peak to peak" wobble in the moon's elliptical orbit about the sun much less than 1%!

Only due to their provincial Earth based POV do people think that the moon orbit the Earth. The more reasonable POV is that the Moon spins 360 degrees on its own axis ~13 times during its nearly perfect ellipse about the sun. The moon would have essentially the same orbit about the sun, if there were no Earth, - still a slightly less disturbed ellipse, with Jupiter being the main perturbations to the ellipse.)

You are still in the mindset that the Earth is the center of the universe and unable to take a more cosmic POV. Too provincial your POV! (and also falsely ignoring fact the moon orbits the sun!)

 

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Etc etc.
Notice the word "functional" in my posts?
I saw (and understood) the explanation on Cluluss' web page.
But (to quote Spock) "a difference which makes no difference is no difference at all".
IOW for all practical purposes it's the same effect...

Rate of rotation has nothing to do with it: look at the mechanical construct. Easy enough to give "Earth" and "Moon" different rates around the same axis.

 

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The answer is "yes". In other words, both points of view are valid. In fact, choosing any fixed point as the center of rotation is fine. Which point of view to use? The one that yields the easiest to manipulate mathematics.

In the case of a free body of constant mass such as the Moon, the point that yields the easiest to manipulate mathematics is the body's center of mass. The rotational and translational equations of motion decouple with this point of view.

Some other point can be handier in the case of an attached body such as a ball on a string or a body of non-constant mass such as a rocket.

 

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The "rigid" models you'r suggestin such as you'r diagram fabricated-from-metal structure... or a solid bar/concrete bridge atachein the moon to earf are false cause they dont represent the moon earf system.!!!

To demonstrtte this... wooud you'r rigid models work for a moon that rotated 2 times per orbit of a planet... no... they woudnt... so why woud you espect a rigid model to represent a system where the moon only rotated 1 time per orbit of its planet.???

Below is a antimated gif showin the diference between a moon that rotates 1 time per orbit an a moon that dont rotate on its internal axis per orbit.!!!

http://cluelusshusbund.250free.com/MoonEarth.html



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Er, they keep one face toward the Earth...

But that's not the case so it's not what is represented.

For the last time!!!
I get it!!
I understand it!!!

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I'm just pointing out... (as D H intimated): to the average guy on the street... get me?

 

Originally Posted by Dywyddyr
Using Cluluss' hardware example of the ball on a string.
One face always towards whoever's spinning it, right.
Where's the centre of rotation for the ball?
Is the ball spinning on its OWN axis or round the user-end of the string?

Ther is only 1 axis of rotaton when a ball is bein swung aroun on a strang... an that axis is at my fangers holdin the strang... esactly the sam as if the ball was atached to a stick an bein swung aroun in a circle.!!!

No i dont get you'r pont... especialy when you say you agree wit my antimated gifs... which clearly show that the moon does rotate 1 time per orbit of earf.!!!

Are you sayin the moon does not rotate on an internal axis.???

 

I'm saying What is the EFFECTIVE difference between your gif and the "mechanical" solution"?*
They both give the same "result".

Just noticed this from BillyT

Actually you're showing the provincialism.
At no stage have I claimed that my "version" is correct.
I'm simply asking what is the EFFECTIVE difference between the two.
As stated above and previously...

I give up

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i would love to see us shoot the moon with a big rope and embed a hook into it. then we can pull the moon closer to the earth.

that would be very interesting. so knowing the rotations of the earth and the moon (supposedly) what would happen if you attached a rope to it from the earth?

 

The sam side of the moon will face earf wit or wit-out a "rigid" connectin arm... but that ant the issue... the issue is... does the moon rotate on an internal axis 1 time per orbit of earf.!!!

I thank we agree that it does... but to be sure... if earf disapeared... do you agree that the moon woud continue to rotate on its internal axis as it orbits the sun.???

 

absolutely. at least i believe that.

 

Nah, the mice that live there would start the rocket engines and move it in a straight line...

Yes. Agreed.
I have NO DOUBTS WHATSOEVER that the moon does indeed rotate on its own axis.
(That last just to re-make the point).

 

check this thread out:

http://sciforums.com/showthread.php?t=90006

 

At last, something of an admission. Like getting blood out of stone.

 

What are you talking about, what "admission" in which post?

 

Remarkable that he would use the phrase 'like getting blood out of a stone', when getting sense out of him is like getting blood out of hard vacuum.:shrug:

 

Billy T said: "You are still in the mindset that the Earth is the center of the universe and unable to take a more cosmic POV. Too provincial your POV! (and also falsely ignoring fact the moon orbits the sun!) "

Why do you say this? My POV is from ANY point in the universe, except the Earth. Your POV is valid ONLY from the Earth.

I even mentioned that the view from Mars shows both Earth and moon are rotating about their own axis.

 

Quite simply because you keep claiming this:

You made (and are STILL making) assumptions about what I'm saying WITHOUT reading what I'm saying.
I.e. provincial because you're only reading what you THINK I'm saying.

And ignored what I was saying.
Never mind.

 

What do you mean by "supposedly".???

Anyhow... assumin that the rope was strong enuff an was atached at earfs equator... the rope woud wrap aroun earf as earf continues to rotate... an in about 10 days the moon coud be pulled into earf.!!!

 

This post.

 

Billy T gone quiet?