Not quite. We need to, in essence, draw a picture of what we're looking at. Once we agree on that, we can attack the problem of explaining what we're looking at.

The existance of the Moon in paleological times can be demonstrated without recourse to mathematical models. By looking at fossil tide lines, and coral growth rings, etc, we can tell 1) the Moon existed back then, and 2) how long the day was.

If we can agree that this is a correct representation of the facts, we can go on to definitions of Physics terms.

You are not using the same definition of torque as the rest of us. At least not the same definition as Doctor Don and I.

I am using my college physics textbook for definitions. It is
Resnick, Robert, et al. Physics, 4th ed. John Wiley & Sons. New York. 1992. ISBN 0-471-80458-4

if anyone cares to check my references, that's the big one.

In chapter 12, Rotational Dynamics, we are shown how torque is the rotational analogue to Newton's Second Law.
force = mass * acceleration
thus
torque = rotational inertia * angular momentum

the torque (tau) acting on a body is given as the vector (cross) product of r and F as

tau = r cross F

where r is the position of the particle from the origin of the reference frame
and F is the force acting on that particle. (The origin of the reference frame I understand to be the center of mass of the body in question.)

Note that there is only one force here. Also note that this is from a physics book, not an astronomy book.

Now, do you agree that my evidence for the existance of the Moon in the deep past is good and useful, or do you deny it?

Do you accept the above definition of torque, or do you wish to propose a different one?

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

from http://scienceworld.wolfram.com/astronomy/Month.html I get the following defs:
I haven't checked your figures for the lengths of the different months, but I'm willing to go with them for now.

Now I'm really confused. How has it not made a complete rotation? From your description it sure looks like it.

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

Precession has NOTHING to do with the decay of satellite orbits. Orbits decay from atmospheric drag!
The direction of launch is totally irrelevant to orbital mechanics. Without a priori knowledge, it is impossible to determine the launch point of a satellite (as long as it is within the orbit "footprint").

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When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-05-05 22:39 ]</font>

Well, you are better off launching them toward the east, though that's kind of a side issue.

__________________
Everything I need to know I learned through Googling.

Yeah, I over-simplified my answer. What I meant, but forgot to state explicitly, was that it is irrelevent whether the launch site is north of the equator (lauching toward the south) or vice versa.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

[quote]
On 2002-05-05 22:37, Kaptain K wrote:
Without a priori knowledge, it is impossible to determine the launch point of a satellite (as long as it is within the orbit "footprint").

Additionally, after being launched into a minimum energy parking orbit, most satellites perform altitude and/or orbital plane changes, completely covering their tracks back to the launch point.

Geo3gh
Quote:
================================================== ====================

Now I'm really confused. How has it not made a complete rotation? From
your description it sure looks like it.

================================================== ====================

Whew! It sounds as if you might be listening. The confusion is the first step, and after that it gets a little scary.

My question to myself at this point is where do we or I go from here?

If you remember correctly my first drawing Recession of nodes .gif

Clearly showed a non connected trajectory.

I almost blew it again and went off on a tangent.
What I've done instead is touch up and re-post the recession of nodes.htm

I added drawing Figure numbers so it will be easier to reference. Could you try to wade through that again please. I know it has some errors, but I'm not sure how to fix them.





Gary

The pictures aren't loading, so that's making it a bit hard to follow. But from the text surrounding the pictures I am getting an idea of where you're going. I think I found some math errors. I can't be certain without seeing the graphics, but I'm fairly sure even so.

Simply put, you have to be careful when dealing with vector quantities. For instance, you have to remember the right-hand rule. If you spin a top anti-clockwise (as you look down on it), the angular momentum is directed upwards. Therefore, when you impart a force to the top, the ang. momemtum is changed, but not in a way that matches one's preconcieved common-sense intuition about how it should change.

For the Moon, you should have 1) a velocity vector tangent to the orbit in the direction the moon is traveling 2) an acceleration vector (due to Earth's gravity) directed towards the center of the Earth, and 3) an angular momentum vector pointed "North".

Since the Earth and Moon are traveling as a system 'round the Sun, I think you can leave out the acceleration due to Solar gravity for now.

BTW, this is in regard to your Fig. 4.

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

Geo3gh
Quote:
<HR>
The pictures aren't loading, so that's making it a bit hard to follow.

<HR>
For sure, the pictures are 90% of it. I checked it out here then again at the B B and It works OK for me. I would say my system is so old that it's only compatible with itself, but I asked my son to check it and it was fine from there.

I've heard your complaint before though, remember this:

================================================== ======================
GrapesOfWrath Posted: 2002-05-02 04:31***
Quote:
<HR>
On the other hand, I just noticed that your drawings are not coming up now, for me. Are they still there?
================================================== ======================

Does any one have any suggestions other than try again?

I would love to move on, but we seem to be hung up way back at step 4 and somehow we need to get to 10.

I know that if you just save the page and then try look at it off line the pictures won't be there. I'm not sure how to glue it together for that, other then e-mailing a zip file.

Jeff,
When you explained about how the top spins weird when you push it, that is kind of what I try show in (Fig 7).


Gary

OK, the pictures are loading today.

Let me quote from your page:
Um. No.

First little nitpick: It would be better to call the blue arrow the Moon's linear velocity.

Let's talk a moment about angular momentum. In the case of the Earth-Moon system, you have three momentums (momenta?). The Earth has an angular momentum due to its rotation about its axis. The Moon has an angular momentum due to its rotation about its axis. And the Earth-Moon system has an angular momentum due to their orbit around their center of mass. Angular momentum is a vector quantity. In this case, all three are pointed "up." Due to the conservation of angular momentum, the sum of these three angular momenta remains constant.

In your figure 4, the Moon is being accelerated towards the Earth by gravity. The Moon's linear velocity balances this acceleration, so the Moon stays in orbit.

Angular momentum does not create centrifugal force. Gravity in this case is the centripetal force. Remember that centrifugal force is a ficticious force.

The rest of your figures veer off from here. With figure 5 you impart an acceleration upwards to the moon. As I said before, you have three angular momenta to deal with, and figure 6 is not taking all the angular momenta into account, so therefore is not an accurate model.

Question: Why do you need figures 1-3? As part of your gedanken, I can accept them, but I think they needlessly complicate the argument. Why can't we start with a force diagram of the moon orbiting the earth? Rather than the hooplah of having them touch then push them tangentally so they get into an orbit. Why not start with the orbit as a given?


_________________
Jeff Schwarz
__________________________________________________
There is a thin line between ignorance and arrogance,
and only I have managed to erase that line.
--Dr. Science


<font size=-1>[ This Message was edited by: Geo3gh on 2002-05-08 14:00 ]</font>

Geo3gh Quote:
------------------------------------------------------------------------
OK, the pictures are loading today.

First little nitpick: It would be better to call the blue arrow the
Moon's linear velocity.
------------------------------------------------------------------------
Great!

That's what I was thinking, but every time I call a circular velocity linear, people get upset. As long as we're on the same page I don't care what the book is called. [img]/phpBB/images/smiles/icon_smile.gif[/img]


Jeff Quote:
------------------------------------------------------------------------
In your figure 4, the Moon is being accelerated towards the Earth by
gravity. The Moon's linear velocity balances this acceleration, so the
Moon stays in orbit.

Why do you need figures 1-3? As part of your gedanken,

Why can't we start with a force diagram of the moon orbiting the earth?
Why not start with the orbit as a given?

------------------------------------------------------------------------
Correct, let me specify (a perfect orbit). Now forget that those drawings might represent the Earth and Moon.

The Moon is not, I repeat, is not in an orbit. You can't call it an orbit it is following an open ended spiral. So it is on a trajectory path.
What I believe necessary is to describe an orbit first so that we can understand how the Moon's trajectory deviates from an orbit. I suppose as long as everyone agrees what an orbit is, and knows the Moon is not in an orbit. We could start at where it says "Not to bad" right after (Fig 7).

I really think we need to know and understand "exactly" what causes precession and recession. By that I mean the unnatural types associated with satellites causing their orbits to get larger (like the Moon) or smaller like most man made satellites.


Jeff
Quote:
------------------------------------------------------------------------
With figure 5 you impart an acceleration upwards to the moon.

------------------------------------------------------------------------
Yes, this is to show a momentum change, (change in direction). A push at near to 90 degrees to the orbital plane will cause a slight speed and direction change. Thus creating an open ended spiral (See Fig 7). This is very similar to what the Moon displays. I was careful not to change the center to center distance. Just the speed and direction. To follow the longer helix the speed needs to increase proportionately.

Did that make sense?
Are we ready for "Not to bad" right after (Fig 7)?


Gary

Well, I certainly disagree. Under that definition, there are no orbits in real life. These are minor quibbles that don't really have anything to do with precession, or the receding of the moon.

It'd be better to try and understand the textbooks.

I agree with GoW. You cannot postulate a definition that is contrary to the accepted definition, then say that the "establishment" is wrong because the accepted definition disagrees with yours.
The Moon is in orbit around the Earth. Just as the Earth is in orbit around the Sun. Whether the orbit is open or closed is a function of the observational referent frame. It is irrelevent to the mathematics of orbital dynamics.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Yeah, if the path of the moon reconnected to its previous position after a month, the Earth would have left it behind! [img]/phpBB/images/smiles/icon_smile.gif[/img]

GrapesOfWrath & Kaptain K



I did get a little radical on you, but I did get your attention.
In my last post I specifically said on or about line 20 something (dependent on browser): "let me specify (a perfect orbit)."


This is the imaginary baseline that I'm trying to establish it is not real. Those two circles are still in a gravity free (other than their own) environment. [img]/phpBB/images/smiles/icon_smile.gif[/img]
Kepler had to change circles to ellipses. I'm just trying to show why the ellipses don't fit together.


The Moon is in orbit; it is just not a perfect orbit.

OR "there are no" perfect "orbits in real life."

Is that acceptable?


Do you guys have some clever way to show and/or prove the difference between recession and precession?


Or does the old hula hoop trick still work? If The hoop is still working do you understand why? Which is it precession or recession?


GrapesOfWrath Quote:
Yeah, if the path of the moon reconnected to its previous position after a month, the Earth would have left it behind!

Or would they crash together?

If the Moon is gravitationally locked to the Moon, and the Earth is moving across space. The Moon would need to go infinitely fast to connect its orbit. The faster the orbit the lower it is.
I think you just described precession and didn't know it. This is what causes satellites to crash down. They are going to fast so they precess and keep coming down.

Kaptain K Quote:
It'd be better to try and understand the textbooks.


Now that is a scary thought!



Let's try to get to (Fig 8 ).

Again it is an unreal condition. If the Moon like mass is moving along the helix at the proper speed then its Nodic and Sidereal months would be equal.



Gary



<font size=-1>[ This Message was edited by: Gary Redmond on 2002-05-11 09:57 ]</font>

The two terms are unrelated, except for similarity of spelling. You might as well ask "is my male sibling a brother or a bother?". Recession means the moon's orbit is increasing in radius. Precession is the response of a rotating or revolving body to a torque applied to the axis of rotating or revolution.

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Kaptain K
Quote:
<HR>
Recession means the moon's orbit is increasing in radius. Precession is the response of a rotating or revolving body to a torque applied to the axis of rotating or revolution.
<HR>


Those are two very good definitions, but there are more. The others are just as good.


Let me do a mental experiment.

Let us obtain 3 identical pendulum clocks, and set them side by side.
Remove the hour hands, and set all the minute hands to 12. Start them ticking (tick tick tick), (tock tock tock).

One hour later stop the clocks; all three hands are back to 12.

These clocks like most good clocks have an adjusting screw on the bottom of the pendulum. On the first clock adjust the screw so that the weight is at its closest to the fulcrum position. Leave the second clock as our control. On the third clock adjust the pendulum so the weight is at its farthest from the fulcrum. Start the clocks.



(tick tick tick), (tock - tock -- tock), (tick - tick - tock - tick)



After the second clock shows one revolution, stop the clocks.

Are all three of the hands pointed to 12?

It would appear that one hand precessed (moved forward), and one hand recessed (moved backward).

<HR>
My dictionary says:



precession-

1) The act or state of preceding, precedence.



recession-

1) The act of withdrawing or going back.



ingress-

1) A going in or entering.



regress-

1) Return or withdrawal.



My dictionary seems to indicate that "precession" and "recession" are opposites. While it doesn't specify the speed up, slow down of rotational motion, that is where it is often used. If you stand in a doorway then step into the house it is ingress. If you step out it is regress or regression.



The Moon both regresses, and recesses; and both are part of the same motion.
You could say; the Moon backs out the door, and around the corner (slowly).



In your above quote you said: "Recession means the moon's orbit is increasing in radius."
I do not agree, but if everyone does then I'll change my story.

Is there anyone out there who knows what you call the "recession of nodes" motion if it's not "recession"?
Is it the "regression of nodes"?



And what do you call "precession" when it is not caused by torque?



A concession, hot dogs, peanuts, popcorn, soda?




Do you hate the English language as much as I do?





Gary

Gary, the trouble you're illustrating with the various definitions is why I recommend that for scientific discussion, Merriam-Webster might not be your best friend. You've got common, everyday usages mixed in with the precise, technical usages. For instance, compare the everyday use of the word "work" with the physicist's use of "work."

One is not necessarily justified in using their workaday understanding for a scientific talk. It may be a good place to start, but if you are thinking in layman's terms when reading a technical post, you can get lost. You have to be careful not to use unrelated technical jargon if you don't want to get lost. For instance, in Computer Science, the prefix "mega-" is generally understood to mean 2²⁰ rather than 10⁶. (Don't get me started on "mebi-".)

Precession, recession, torque, etc., all have specific definitions as used in this forum, and one needs to be careful in their use.



_________________
Jeff Schwarz
__________________________________________________
There is a thin line between ignorance and arrogance,
and only I have managed to erase that line.
--Dr. Science

<font size=-1>[ This Message was edited by: Geo3gh on 2002-05-13 20:40 ]</font>

For definitions relevant to this site, I like to look here.

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