As GOW pointed out, Dapted's figures don't quite add up here. My point of contention, however, is this whole Earth-Moon touchy thing. When did that spring up? I've never heard of any such wild fantasy except in this thread. Generally accepted theory is that the Moon came into existence when a "Mars-sized object" collided with the Earth during the dawn of Solar System history. If you accept this theory then there's no need for any bizarre Hector-like image of a touching Earth and Moon that then began receding from one another. Even if you doubt this theory, you're not left with any real option other than the Moon being a captured body - which also removes the need for any Earth-Moon cheek to cheek dancing.

Another elementary point: The dinosaurs became extinct some 65 million years ago (certainly not as recently as 1.5 million years ago), so I think we can rule out the possiblity that they were squished by an overly affectionate Moon.

Cheers,

JB

__________________
Nowhere in all space or on a thousand worlds will there be men to share our loneliness. ...in the principles of evolution we have had our answer: of men elsewhere... there will be none, forever. - Loren Eisely, The Immense Journey, 1956.

I've been staying out of this for various reasons, but I must jump in here. I smell a whiff of creationism...

You cannot extrapolate the Moon's current recession speed (4 cm/yr) back in time very far. The current rate of recession is known to be high because of a peculiar resonance with the ocean; the friction caused by the moving tidal bulge is very high right now. In the past, although the Moon was closer, the actual amount of friction it caused by tides was smaller. The efficiency with which the Earth's spin energy was transferred to the Moon was lower, and so the Moon's recession rate was slower.

Extrapolating the Moon's recession rate backwards using a constant velocity is therefore an incorrect method. This has not stopped creationists from using it, however, to "prove" the Moon cannot be more than a few million years old, not billions. I am unsure how this helps their cause, of course, since that is still more than 6000 years. Nonetheless, I get a bit antsy when this argument is used. For more, check out talk.origins.

<font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-04-01 00:33 ]</font>

Done

I think someone else mentioned the speed-up that a skater experiences when they bring in their arms. How is that reconciled with your view of basic physics? It seems to be a counterexample to your way of looking at things.

It's not much of a hurdle for me at all. Just ask the BA.

Actually, the analysis in those physics books that you think might be wrong does assume that there is no loss of angular momentum. In tidal slowing, as those dastardly physicists tell us, the angular momentum stays the same. Check it out.

This is my last try, and then I'm giving up.

I know you were responding to Grapes of Wrath, but I would just like to point out that I have not quoted any books; I have showed you the actual math. You'll get no argument from authority from me!

Just short ones, then.
1) yes.
2) no. Centrifugal force is a fictional force invented to account for the *apparent* outwardly directed force when the observer is in a rotating reference frame.
3) yes.

This "law" only holds (and I don't know that I'd call it a "law", per se, as it's really just a restatement of the obvious fact that if the internal forces did not sum to zero, the object would fly apart. Therefore, for an object which is not flying apart, the forces must sum to zero. QED.) if the system is in equilibrium, which the Earth-moon system is not. Besides which, Force != Torque, as I have mentioned already.

No.

No. Where do you get this stuff? A torque is nothing more or less than a force applied at some offset vector to the center of mass of a system. You only need one force. r cross F, as I have now told you three times.

No. *linear* momentum is not conserved. *angular* momentum is conserved.

There isn't one because you don't need one. You still haven't addressed what "secondary force" you think is involved in the non-zero torque on the spinning ice skater.

I'm sorry, but this is just flat-out wrong.
I've demonstrated both mathematically and through example that it's wrong. You haven't refuted (or tried to refute) either my math or my example, so I must conclude that this conversation can't go any further. I wish you luck clearing up your confusion, but as long as you insist on holding onto false premises, I don't think you're ever going to get anywhere.

Yours sincere,

Don

I agree with Don about this not going anywhere. Gary is not responding to either Don's questions of where the "other" force is coming from in the ice-skater example, nor has he answered my questions about the evidence.

Hopefully Gary will repond to our specific questions, and not simply trot out his lumber example again.

__________________
Jeff Schwarz
__________________________________________________
Argh!! They booby-trapped their sun!!****--Invader ZIM

[Jeff Schwarz
Said:
Hopefully Gary will repond to our specific questions, and not simply trot out his lumber example again.
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Originally it was not my intention to respond to things like this, but to you as author of this thread, I feel an obligation.

1) Ice-skater example.
An Ice-skater eats their "Wheaties" (external) that supplies the electricity, to cause thought, to control, and nourish muscle.

2) Questions about the evidence.
I'm somewhat confused, are you talking about the layered tidal sands and corals that were formed *long* before the Moon could have even come into orbit? I was quite sure that the first thing we needed to do was find out when the Moon arrived in orbit.

3) Don's questions. SUCH AS SEE PREVIOUS POST
Quote: You haven't refuted (or tried to refute) either my math or my example, so I must conclude that this conversation can't go any further.
I have tried to explain that the math, regarding a torque, applied to an inertial mass, by a gravitational force, requires a secondary force. I thought the lumber yard thing would work. [img]/phpBB/images/smiles/icon_frown.gif[/img]
Try this: Walk over to the closest (hinged door) open or close the door. That is torque. It takes one force to move the door, and one to hold it to the wall or hold the wall up.
Newton's universal law of gravitation has what might be called an addendum, which goes like this. "A further property of gravitation is that the gravitational force obeys the law of superposition." And. "That is, the force between any two bodies is unaffected by the presence of other bodies."

xxxy
xxxx o
zxxx

If you let the x's, the y, and the z represent Earth, and the o the Moon. You will find that gravitational force between y and o can not affect the force between y and z. Inversely the force on z by o will not affect y.
If the parallelogram xyxz were to rotate it would need to be due to something other than o.

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Kaptain K
Posted: 2002-03-31 22:45***
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So Gary, You are right and every PhD Astronomer, Geophysicist, and Mathematician in the world is wrong. What, exactly, are your credentials that we should believe you over them?

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Fantastic.
Kaptain, I must compliment every one who thinks.
Please leave the Geophysicists, and Mathematicians out of this.
I have no credentials. I never went to your fancy schools. Perhaps the only things going for me are these; I read, I think, and I won't lie to you.
Last night I posted a message here. This morning I found every one angry at me. It has been my experience that 90% of all anger, comes from fear. What are you guys afraid of? I don't want your jobs I have grandchildren to raise. I have asked several times that you do the math. All you do is quote the books and tell me I'm wrong or imply worse. [img]/phpBB/images/smiles/icon_frown.gif[/img]
It looks to me as if only one person has tried the math. They (dapted Posted: 2002-03-29 01:50) came up with 1.5 million years which BTW is wrong and you may remember I suggested a slight correction.
I know this is repeating myself, but I need to know if you heard me.
The Moon is moving away from the Earth along a vector. That vector is not just the 3.8 cm per year, but must also include the recession of nodes motion of 1 revolution every 18.6 years.
Is that, or is that not correct?
Could someone (with credentials) please get out a chalkboard and tell us if that is correct?

To solve a problem you must define it correctly.
I could waste my time and try to answer all the negative comments, but an answer to the above will due for now.


Gary

I inserted dots to be empty space, otherwise the parallelogram seems to turn into a square on my display, and the moon rushes up to earth adjacency...

Note that y is closer to o; by the inverse square law, it is more attracted. z is farther away, and by the isl, is less attracted -- and, in fact, is so much less attracted that it does not compensate for the additional attraction felt by y.

Thus, the force drawing y toward o is unbalanced, overall. Assuming that, due to orbital velocity, the overall p-gram does not actuall draw nearer the moon, it will, at least, rotate until y is closest to the moon.

Do the math: Fyo^2 :: 170 Fz0^2 :: 383

Is anyone good enough to do a simple BASIC sim? (I think I am, but I'm not wholly sure...)

Silas

General Mills is an external force?

That much is true, but...

That is not. o does cause a torque on the other figure. That is easy to calculate.

I did.

The way I remember it, not only did I also do the math, I corrected dapted's. You can look it up. I even showed my work.

I have an MS in math, I'm ABD in Geophysics, specializing in the shape of the earth. But credentials aren't important.

Because I have done the math.

I'm going to take this somewhat out of order.

I'm not angry with you. I disagree with you, but that's all. When I'm angry I tend to avoid replying, since it would tend to consist mostly of deleteables. [img]/phpBB/images/smiles/icon_smile.gif[/img]

But on to answering your points.
Hmmm. Maybe this is something we agree on. Maybe not.

So an ice-skater gets on the ice and starts to spin. Then, she pulls in her arms and legs, and due to conservation of angular momentum, she spins faster.

Sure, it takes food to get the energy to get on the ice and do all this, but once she gets spinning that's it. Pulling in her arms is negligible in terms of the energy that's already in her spin. Simple conservation of ang. momentum is all that's needed to speed up her spin. No external energy is needed.

Do we agree on this?

If so, then the same applies to the Earth-Moon system. If the moon is getting farther away (and we can see that it is with the lasers bouncing off the Moon) then it [bold]has[/bold] to be going slower. Simple conservation of momentum.

One basic interpretation of the tidal sands, given the size of the tides they suggest, is that the Moon existed to cause them. They are too large to be accounted for by the effect of the Sun's tides. So we take those tidal sands as evidence of the non-trivial issue of whether or not there was a moon in orbit.

As for the corals, they don't speak to the issue of the Moon per se, but they do indicate the number of days in the year. If you take the number of seconds in a year to be roughly constant, then the length of the day has to have been shorter.

Any theory counter to the prevailing one should explain the length of the day in the Devonian period.

Point taken. I don't have time right now, but I'll do the math soon. Possibly tonight.

If I'm taking you to task for not answering my issues, the blade cuts both ways.

[/quote]
I have tried to explain that the math, regarding a torque, applied to an inertial mass, by a gravitational force, requires a secondary force. I thought the lumber yard thing would work. [img]/phpBB/images/smiles/icon_frown.gif[/img]
[/quote]

I disagree with your analogy. When you deal with a piece of wood compared to the Earth, then you can assume point masses, since the tidal effects will be negligible.

As for the Earth-Moon system, things get more complicated. When you describe the orbit, you can treat them as point masses orbiting a barycenter. That's fine. But from the near side of the Earth to the far side, the Moon pulls differently. It pulls harder on the near side of the Earth than the far side. This deforms the Earth. The bulge then gets tugged on causing a torque.

You don't need an external force to cause a torque. You just need a difference in forces.

Imagine a merry-go-round that is not fixed to the ground. It just pivots on a spike, like a top. I come a pull to start it spinning. I just added torque.

What was the "other" force holding it?

That's not a great example, but the best I can do on short notice.


I'll play with the math later.

__________________
Jeff Schwarz
__________________________________________________
Argh!! They booby-trapped their sun!!****--Invader ZIM

All merry-go-rounds are not fixed to the earth, but pivot on spikes.

So let's take one that's stationary. You pull on it to start it spinning: by the laws of conservation of angular momentum, the earth takes on a (small!) contrary spin.

The energy comes from your biological energy, and ultimately turns into heat. The same is true for the friction of your feet against the ground, and your hands against the merry-go-round.

The m-g-r's inertia resisted your efforts; ordinary Newtonian F=ma explains just about everything here.

What's your point?

Silas

Silas.

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I inserted dots to be empty space, otherwise the parallelogram seems to turn into a square on my display, and the moon rushes up to earth adjacency...

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Thank you.
I'm old, but new at this BB computer stuff. My $5 a month on line doesn't let me proofread and set type as I should. I'll try to remember the picture hint. Perhaps I could store a .gif and leave a url. ???? Build my own chalkboard. [img]/phpBB/images/smiles/icon_smile.gif[/img]


Geo3gh quote:

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Hmmm. Maybe this is something we agree on. Maybe not.

So an ice-skater gets on the ice and starts to spin. Then, she pulls in her arms and legs, and due to conservation of angular momentum, she spins faster.
No external energy is needed.

Do we agree on this?

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Hum.
The arms and legs must be pulled inward against the outward acceleration created by the rotation (centrifugal force). The energy for that was chemically stored from an external source. "Wheaties"
I still think the energy has to be called external.

Quote:
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If so, then the same applies to the Earth-Moon system. If the moon is getting farther away (and we can see that it is with the lasers bouncing off the Moon) then it [bold]has[/bold] to be going slower. Simple conservation of momentum.

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Yes, maybe, most definitely.
This is where it gets tricky.
In your above paragraph you used the word slower not slowing that makes you absolutely correct. Now for the question of slower than what, and in relation to what.
Let me start with the Sun. The Sun has a mass nearly 330,000 times that of Earth. The Earth has a mass more than 81 times that of the Moon. All 3 of these bodies are going in the same general direction around the Galaxy. The Sun goes in what might be called a straight line at a more or less fixed speed. The Earth on the other hand follows a helix at almost 90 degrees to that line. Once a year when the Earth crosses an imaginary line to the stars, we find the Earth to have fallen behind by 0.68 seconds.
My first question is: Was it Earth's axial rotation, helical rotation, or the linear movement around the Galaxy that caused the leap second?
Next.
The Moon follows a helical path about 5 degrees tilted from the plane formed by the Earth's helix. Again, once a year it is found that the Moon has fallen away from the Earth 3.8 cm. If I get this wrong please don't take my head off. In that same year, the 5 degree tilt recesses or backs its way 1/18.6 of the way around the Earth.
Second question: Was the 3.8 cm measured along the helix or the Galactic linear?

This is my (one man's) opinion. Because the Moon is so close to a huge mass (Earth), and because the Earth is so close to a huge mass (Sun) the helical speeds are fixed. Because the Sun is so massive it is slowly trying to move away from the Earth. Likewise the Earth is moving away from the Moon, but that motion is in a linear direction around the galaxy.
As you said: Simple conservation of momentum.

The Moon is not slowing.
The Earth is not slowing.
They are just going to slow to keep up with the Sun.

PS And you thought you lost sleep!

Quote:
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length of the day in the Devonian period.

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First things first.

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GrapesOfWrath
Quote:
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The way I remember it, not only did I also do the math, I corrected dapted's. You can look it up. I even showed my work.

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Yes, and you were wrong. [img]/phpBB/images/smiles/icon_frown.gif[/img] You only used the 3.8 cm. The vector that the Moon follows includes the recession of nodes. See my discription above.


Gary

And I tried to explain that the lumber analogy was flawed. I thought an integral/sum would work, being the simplest way to break down the problem, but apparently not. I tried providing an example of a torque with no secondary force (I provide another one below), since you only need to provide one example to disprove necessity, but that didn't seem to stick, either.

Try this: put your piece of lumber on a slick ice-rink (just after the Zamboni goes by) and kick it on the side at one end. It will slide away from you, spinning. *One* force (your foot hitting it), and there is torque.

What your door analogy misses is that the door would still spin "open", even if there were no force to hold it to the wall. You don't need two forces. The *net* force (vector sum of all forces acting on the object) just has to be not pointed at the center of mass. That's all you need.

True, in the Newtonian limit, but irrelevent. Silas covered this perfectly well already, so I won't repeat.

I agree with Gary. Arguments by authority are irrelevant. Let's stick to the math.

FWIW, I'm not angry, just baffled and frustrated.

And I would like to point out (again) that I have not quoted a single book.

And that's all I have to say about that.

Don

Darn it. Don beat me to the lumber on ice example. I was thinking of that on my way home.

I retract my merry-go-round example, since it doesn't do what I want. Please ignore it.

__________________
Jeff Schwarz
__________________________________________________
Argh!! They booby-trapped their sun!!****--Invader ZIM

Didn't Velikovsky have Venus smacking into the Earth and stopping it from rotating, then returning and starting it up again?

That may be a good idea. I'm thinking of doing the same thing. Sometimes the ASCII art just doesn't get the point across.

I think we're talking at cross-purposes here.

Yes, she needs fuel to pull her arms in. But if I'm not already spinning, pulling my arms in does not start me to spinning.

But if I'm spinning with my arms extended, I will spin at some rate R1. I pull my arms in, and I spin at an increased rate R2.

If I pull my arms in linearly towards my center, how is this causing me to spin faster? I say that it is due to conservation of angular momentum. Is it your position that the energy used to retract my arms is also translated into pushing me to rotate faster?

My position is that the energy used to pull my arms in only effects my arms. It does not add extra energy to my rotation. The energy in my rotation is constant. But since with my arms pulled in I have a smaller inertia, my rotational rate has to increase to keep the energy the same.

I give this link as a description of angular momentum and its conservation:

http://theory.uwinnipeg.ca/physics/rot/node7.html

and while I'm at it, here's something on Torque:

http://scienceworld.wolfram.com/physics/Torque.html

(The only reason I'm putting the links here is so you and I have a common set of definitions and equations. These are what I am using. Do you wish to use other definitions and/or equations?)

__________________
Jeff Schwarz
__________________________________________________
Argh!! They booby-trapped their sun!!****--Invader ZIM

Just to provide a little "dressing" to this lunar "salad" thread - here is Bonestell's old 1952 LIFE magazine cover depiction of the early Moon as seen from Earth. Looks very close as seen from Earth billions of years ago, and before life. (Including LIFE magazine.) [img]/phpBB/images/smiles/icon_wink.gif[/img]

And here is his painting of the Earth - Moon system forming within the early disc of the solar system.

I know this doesn't contribute much to this thread. It's just fun to look at. Bonestell is speculating in a creative way.

Chip