Why Is The Moon Not Spinning Then?

I think he means you're full of shit.

Not my opinion. I don't have one on this issue. Just trying to help out with translation difficulties and inject a minor amount of humour. Have you upset him previously?

 

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Nope. Don't even know the dude/chick (dude + chick = dick???).

Anyway...

 

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To an outside observer the object in the bearing does not rotate.

 

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That question is the sort of thing a high-school student should know how to answer.
If a first-year student had no idea, he'd probably fail the rest of the exam.

What happens if instead of a solid metal bar, it's made of something bendy like a soft plastic say (with a significant spring constant)?
How would the relationship described in part ii change (starting with the upright pendulum in SHM case)?

 

Ken:

Enough of this with orange in your hand nonsense, which all distant observers see as spinning about its polar axis. Just explain the OBSERVED librations of the moon (or the multiple 360 rotations about its axis it would have at apogee if torque-free scattered into the 50 month orbit by a passing third body.)

Or answer Janus58’s question asked long ago but now twice repeated without drawings for you to attack in your posts.

I.e. You agree that a planet’s moon could be spinning about its polar axis if that spin axis is in the plane of its orbit. (There is no way that can be attributed to spin about the barycenter.) If the polar spin axis is tilted up 1 degree from the orbit plane, or 2 degrees up etc. it is still spinning about the Polar axis, yet when 83 degrees tilted up, as the Earth’s moon is, according to you, it is not spinning about its polar axis. “It is only rotating about the barycenter.” At what number of degrees up tilt did it stop to spin about it polar axis?

The reason you continue to ignore these two different questions, both repeatedly asked, is that they are facts of nature INCOMPATABLE with your false POV.

 

Moving at a steady rate it will not rotate out there. However, if you accelerate it, then it will spin until slowed by friction. Once friction has stopped its rotation, then some sort of force would need to be applied to re-spin it.

E.g., take a bicycle wheel and grasp its axle with both hands, and hold it axle up (wheel parallel to the ground), and start spinning your body counter-clockwise, and the acceleration will cause the wheel to spin clockwise (as viewed using the right-hand rule.)

If you keep spinning your body, then friction will soon stop the wheel from spinning, and when you decelerate your body's spinning, the wheel will then reverse direction and spin the other way, until again slowed by friction.

While you're still spinning your body 360˚, and after the wheel stops spinning 360˚ on its axial (from friction), you of course will then be viewing a non-spinning wheel since some force would be required to start it spinning again.

HOWEVER, an observer watching you (a *sidereal observer *) will still see the wheel *appear* to spin 360˚ once each time you spin your body around 360˚, even though for you in the center position, the wheel has stopped spinning.

Of course, the wheel (like the moon) stopped spinning on its axis due to friction, so the wheel's only remaining 360˚ movement the *sidereal observer * is actually viewing would be the wheel now revolving around your body's center of mass and NOT any circular 360˚ rotation around the wheel's own axial.

Billions of years ago when it formed our moon didn't start spinning on its polar axis due to orbital acceleration as the bicycle wheel would spin when accelerated in a circle, but a similar force may have started our moon spinning, much as an ice-skater accelerates her spin around her body's mass when she pulls her arms closer into her body:

"The Earth spins on its axis because of conservation of angular momentum. The classic example of this is a figure skater. When a figure skater pulls in her arms, she spins faster. The Earth formed when gas left over from making the Sun condensed into the planets. As this gas cooled and condensed, it started to spin faster. Now that it is spinning (and not condensing any more), it will keep spinning at a steady rate unless something stops it."

(add HTTP): imagine.gsfc.nasa.gov/docs/ask_astro/answers/961107a4.html

If the moon didn't form when spinning dust aggregated under the force of gravity, then an Earth collision with a large astronomical body may have started the moon spinning – no one knows for sure how it started rotating, just that the moon likely did at one time rotate around its polar axis.

Regardless of how our moon started rotating around its polar axis, billions of years ago tidal braking (friction) quickly stopped the moon's polar rotation, just as friction stopped the bicycle wheel, so today our moon ONLY orbits (or revolves) around the Earth.

Just like the bike wheel in that demonstration, our moon succumbed to friction and stopped rotating on its polar axis. Today, the moon only orbits. Case closed!

Of course, we have other viewpoints here from the spatially challenged:


I am Superluminal of the Alien clan of Usa, Nordamerica, a Terran, of Sol, and I say:

INDEED!

 

Up until now Ken, you have appeared stubborn. This is not a bad quality. (In some reference frames it is called confident and strong willed.) However, you have now blatantly failed to answer this:

Now it is clear that you are evasive. (In some reference frames that is called dishonest.) Now prove me wrong by answering the questions.

 

Someone forgot to add a couple of things:

 

---snip from Ken's Post 94---
A simple demonstration - draw a happy-face on an orange, then go into a darkened room and take the shade off of one table lamp (that will be the sun), then hold the orange on your outstretched palm with the happy-face facing you, then spin 360 around counter-clockwise on your heels.

If you do that, then you'll see all phases of the moon likewise pass across that orange.

The orange will NEVER spin in your hand, yet, its happy-face will always remain pointed towards your spinning body!

You can even see more than 50% of the orange's surface (libration) by raising the orange/moon model above and below your eye level. Viewing the orange/moon first with one eye and then the other eye will also cause some libration (caused by parallax.)

When you show a person that demonstration to prove that the moon doesn't spin on its polar axis (only around your body's axis), they will either grok it, or they'll dig their heels in and claim your arm isn't the same thing as gravity.

Of course an arm isn't gravity, but in an accurate model your arm can serve the same purpose.
---/---

You say that, "all that means is that {the orange} is moving and rotating with your hand?"

OK, but if your hand and orange were both rotating around the orange's center-axis (instead of ONLY around your body's axis as I claim), then wouldn't that hurt when your hand snapped off at the wrist and started rotating along with the orange around the orange's axis?

OR, are you claiming a different spin axis than the orange's center axis?

Trippy, there are only two possible locations for a spin axis in this demonstration, either the orange spins around its own center-mass, or around your body's mass.

If you want to spin the orange around two axes at the same time, then try it again, but this time use your free hand to keep the orange pointed at the same wall as you spin your body 360˚ counter-clockwise. What happened?

From your center-point perspective, did the orange rotate one time clockwise, even though the orange didn't rotate from the sidereal perspective since it remained facing the wall? That's the 0:1 spin ratio. Spin the orange 1.93 times clockwise as your body rotates counter-clockwise, and that's Venus' spin ratio, a .93:1.

Spin the orange clockwise a tad faster to rotate it a full two times per each 360˚ counter-clockwise spin of your body, and you'll have another 1:1 spin rate, the same 1:1 rate you'd have if you stopped rotating the orange and just spun your body 360˚ counter-clockwise.

Isn't that interesting, that you can have two 1:1 spin rates on both sides of a 0:1 spin rate when astronomical bodies spin down from the clockwise direction? That's basically what Venus is now doing, so it's more than a hypothetical spin-down!

These demonstrations work better if you're honest about the results, and if you also let the results make you think about these relative motions, which are difficult to fully grok until you actually try doing these simple moon models.

Ken

 

Depends if it's free to move around another axis. If I'm standing with an outstretched hand with nothing on it, it's stationary wrt me. If I start revolving (spinning, rotating) because I'm on a platform that turns, my hand turns too.
If I move my wrist from side to side, or up and down my hand turns some more - there's a name for that I think you should know (hand waving). Although it's a conscious movement it does model what an elastic bar would do in SHM, and it models what the earth-moon system does: librate

You're getting a sore head by now, surely?

 

A perfect bearing does not have friction.

 

A perfect frictionless bearing would still need some force to either start or stop it.
E.g., the Earth & moon have the braking friction caused by gravity.

Even though astronomical bodies have potential frictionless axes, all are subjected to tidal locking (friction) to some degree. Jupiter, is so far from the sun, and so massive with relatively tiny moons, that not much tidal-braking force has been applied to Jupiter over the eons, so Jupiter still retains most of its original rotational speed.

If the bicycle wheel had a truly frictionless bearing, then air resistance would eventually stop the wheel from spinning.

If you had a non-spinning wheel with a frictionless bearing in a vacuum chamber spinning at the end of a boom, then it would still likely need some exterior force applied to the wheel to start it spinning.

Ken

 

My example was going to move on and ask more questions that would hopefully make you understand, but I'll not bother.

 

Good. Everyone should stop providing new analogies for Ken to discuss and thus allowing him to post but avoid two OBSERVATIONS, which are irrefutable proofs that his POV is silly. Namely KEN CAN NOT:

(1) Explain the OBSERVED libration of the moon.

Or

(2) Tell the tilt up angle at which a moon initially spinning about its polar axis in its orbit plane switches to spin ONLY about the barycenter as the polar spin axis is tilted up.*
-------------------------
*The moon's polar spin axis is tilted up about 83 degrees. For Ken's POV not to be nonsense, conflicting with observations, requires the polar axis of the moon be exactly perpendicular (90 degrees tilted up from the orbit plane.) There is also the latitudinal libration observed and it is caused by the not 90 tilt up of the moon, but is also small. Little wonder Ken has avoided answering either question despite many of us asking several times.

I also asked (1) differently in several ways, including imagining a third body rapidly passing near moon scatters the moon, without applying any torque to it, into a much more elliptical orbit with 50 month period. Then near apogee, when it orbital advance is much slower, it unchanged 360 degree in 28 days turning makes it show all sides to the Earth at least a dozen times (I.e. clearly is spinning about its polar axis in an “extreme libration”) – Moon is in an almost circular orbit so the current libration as it spins around the polar axis only shows about 59% of the surface to earth. To see more by larger libration, the eccentricity of the orbit must be larger. The size of the longitudinal libration increases with eccentricity, but LIBRATION IS CAUSED BY SPINNING ABOUT THE POLAR AXIS with a constant spin rate, which cannot be same as the changing orbital angle advance rate as moon goes around the elipse of its orbit.)

Ken is just a stubborn fool, and a dishonest one too, as long as he ignores these REAL OBSERVATIONS and speaks only of oranges in his hand, etc.

 

Each planet & each moon (that we know of) revolves around another body. Each 1 burmolnes except Earth's moon. Why doesn't Earth's moon burmolne???

 

burmolnes??

 

Well, the earth and the sun create the same gravitional cycle which results in the completeion of a cycle every 638 miles every 15 minutes.
These two motions result in a hap hazard motion of the moon, referred to as liberation, where at times as much as 59% of the moon surface can be seen of a assumed 30 years.
the build up or decrease of the cycyles causes for various motions of the moon.


DwayneD.L.Rabon

 

This is either very subtle and clever, or very dumb and stupid. Waiting to find out which is quite exciting.

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Dwayne, I do not think your hearing well any more. The lunch bell at your institution has already rung. Better get there before they stop serving.

Run along now, and take Ken with you.