Re: Orbital precession w/o GR

On Fri, 30 Nov 2007 14:12:32 -0000, "JMA" <NOSPAM@xxxxxxxxx> wrote:


"Eric Gisse" <jowr.pi.nospam@xxxxxxxxxxxxxxxx> escreveu na mensagem
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On Fri, 30 Nov 2007 01:27:56 -0000, "JMA" <NOSPAM@xxxxxxxxx> wrote:


"Eric Gisse" <jowr.pi.nospam@xxxxxxxxxxxxxxxx> escreveu na mensagem
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On Thu, 29 Nov 2007 16:13:05 -0000, "JMA" <NOSPAM@xxxxxxxxx> wrote:


"bz" <bz+spr@xxxxxxxxxxxxxxxxxxxx> escreveu na mensagem
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"JMA" <NOSPAM@xxxxxxxxx> wrote in
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What is really a mystery is how people talk about
precession of mercury orbit, but nobody has any idea
what precession is

[quote http://www.thefreedictionary.com/precession]
1. The rotational motion of the axis of a spinning body, such as the
wobbling of a spinning top, caused by torque applied to the body along
its
axis of rotation.
2. The motion of this kind made by the Earth's axis, caused mainly by
the
gravitational pull of the Sun, Moon, and other planets. The precession
of
Earth's axis has a period of nearly 25,800 years, during which time
the
reference points on the equatorial coordinate system (the celestial
poles
and celestial equator) will gradually shift their positions on the
celestial sphere. The precession of the equinoxes is the slow westward
shift of the autumnal and vernal equinoxes along the ecliptic,
resulting
from precession of the Earth's axis. See also nutation.
[unquote]

For instance:
A 3 years old kid knows very well what light is.
But a 3 years old kid knows nothing about what light really is and
how he can be fooled by light.

Some facts about precession:
1 - Constant precession requires constant torque.

No, it does not. Study rigid body motion.

Funny, it is you that needs to study rigid body motion.

Yaaaaawn.

I have gone through the rigid body mechanics sections of both
Goldstein and Symon. You still don't know what you are talking about.

Those books are very limited on the topic.

Yea, if you don't count the dedicated chapter Symon and the TWO
chapters in Goldstein dedicated to rigid body mechanics. You clearly
have never even opened either Symon or Goldstein, much less seriously
studied either.

I've already send you the PDF file with the most advanced
deviation on the topic.

Goldstein and Symon are better. I can make this judgement because I
have studied both and can say their treatment of rigid body motion is
more extensive.



Look here, let:
Precession angular velocity be (omega)p
Torque be T
Main angular velocity be (omega)3
Inertia moment along the main spin axis of the rigid body be I3.

Then,
(omega)p = T / (I3(omega)3)

Since I3 and (omega)3 are constants, even a 10 year kid
will see that when torque changes the angular precession
velocity changes too.

Wrong as usual. Time for you to open a classical mechanics textbook...

Read page 32, equation 8.75.
You are a liar.

JM...JM...JM...

A special case proving your point does not mean you are correct. The
/counterpoint/ to your argument is the torque free rigid body whose
precessional velocity changes as a function of time. The derivation of
which is in both Symon and Goldstein.



The body axes are NOT the same as the axes in which a body precesses,
rotates, and nutates.

What a moron.
You simply show you ignorance whenever you say something.
If the bosy doesn't precess around its principal axis (rotating
axis fixed to the body) around which axis does precession occur?

Key words: rotating axes fixed to the body. Those are not the same as
the body axes.


I don't know if you are just ignorante, or a compulsive liar.


Where is the constant torque? The torque is highly variable.

Strawman, and the argument is motivated from classical mechanics.

You always dance with rotation of the rigid body.

Why do you continue to think you know what you are talking about when
two textbooks on classical mechanics explicitly disagree with you?

You never pointed anything that could disagree with me. Ever.
You just say and never show nothing.

Selective memory is a beautiful thing. You must be a happy person
since you can forget, at will, anything you don't like.



2 - Where does the kinetic energy come from?

I believe kinetic energy comes from the kinetic energy fairy.

Since energy maust be conserved, please tell me where
the precession kinetic energy comes from.

Why do you continue to harp on the "WHERE DOES THE ENERGY COME FROM?"
thing?

Because it doesn't come on your nice books.

Except it does. The work-energy theorem specifically and energy
conservation in general is something harped upon long before any
student hits rigid body motion.

Since you don't know nothing besides copy/past from
books, no surprise you have no clue and always dance with
questions that require understanding of something.

Again:
"WHERE DOES THE ENERGY COME FROM?"
I've already explained to you, but you cannot learn.

You make the false assumption that it has to come completely from the
potential energy of the system. You forget that the body can simply
put some of its' kinetic energy /somewhere else/ - slow down one part
to speed up another part.

Go back and study the freely rotating rigid body for a simple
demonstration of this.



The kinetic energy comes from the potential energy.

Nope. The sum is conserved and there is an interchange of the two but
that does not mean one comes from the other.

What a moron.
The energy conservation Law requires that the sum is conserved.

I can prove this - can you?

Look, moron.
It was you who said:
««Nope. The sum is conserved and there is an interchange of the
two but that does not mean one comes from the other.»»
First you said NO, now you say YES.
Make up your mind, explain what you mean, or else go away.

You forget the third possibility which I have just explained and you
have never considered.



(always at any instant) and this repeats over and over around
all the physics.

You have kinetic energy involved (increasing) and no other
source for energy then potential.

Whenever you want to talk physics you show the bluff you are.

Tried it before - you didn't understand. My study of classical
mechanics has continued - have you looked at Symon or Goldstein yet,
or do you still think you don't need to look at a book?

Books are good for learning.

Then why do you refuse to look at the ones I suggest?

After reading and learning it is time to understand.
Once you understand the subject you can talk about it.

So, please, say what you have learned, ONLY.


You probably still don't understand how to properly construct a
Lagrangian for a system.


Come on, let me laugh more on you and tell me where the
precession kinetic energy comes from.

Kinetic energy fairy.

Ignorant.

Stupid question, stupid answer.



Since energy is conserved, potential energy needs to be
dissipated. That is, a smaller secondary motion, called
nutation, occurs.


If you knew that planets orbit in a plane and understood what nutation
is you would see why what you said was really, really stupid.

Nutation is the motion orthogonal to precession and both of
them orthogonal to the main spin axis.
I bet you going to say, no it isn't !
(plus the usual crap, learn ... bla-bla.)

Actually that is correct. Now explain to me how a planet nutates even
though it moves in a plane.

The plane of the orbit precess and nutates.

Nope.

The plane of the orbit is fixed. That this is true is a 2 line proof
assuming constant angular momentum can be assumed. If you can't, it
expands to a 10 line proof.

dL/dt = 0

The orbital plane is thus fixed.


It is the plane of the orbit (like if it was a rigid body - remember
rigid body?) that precess and nutates.

Nope. Planetary orbits are not like rigid body motion.



For you nutuation is only a sound word.
Tell me something more about nutation.


.

Relevant Pages

  • Re: Orbital precession w/o GR
    ... precession of mercury orbit, ... The rotational motion of the axis of a spinning body, ... The motion of this kind made by the Earth's axis, ... I believe kinetic energy comes from the kinetic energy fairy. ...
    (sci.physics.relativity)
  • Re: Orbital precession w/o GR
    ... precession of mercury orbit, ... The rotational motion of the axis of a spinning body, ... The motion of this kind made by the Earth's axis, ... I believe kinetic energy comes from the kinetic energy fairy. ...
    (sci.physics.relativity)
  • Re: Reason for Procession of the Equinox?
    ... > precession itself. ... That is a slight clockwise motion of the top's axis. ... that spin interacts with the direction of gravity's pull. ... over to the Earth and the Moon. ...
    (sci.astro.amateur)
  • Re: [Embedded troll] Easy Questions
    ... "The reason Precession occurs is that the Earth not only ... rotates on its axis -- otherwise known as the Axis Munde ... equinoxes or the great year in a comprehensive dictionary. ... "The Earth's rotation axis is not fixed in space. ...
    (comp.arch.embedded)
  • Re: Orbital precession w/o GR
    ... nearest approach to the sun along the orbital plane," whatever the ... there was still some 'precession' left over. ... Why are you confusing rigid body motion and orbital motion when you ...
    (sci.physics.relativity)