Re: Orbital precession w/o GR


"bz" <bz+spr@xxxxxxxxxxxxxxxxxxxx> escreveu na mensagem
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"JMA" <NOSPAM@xxxxxxxxx> wrote in news:5r86onF11tfvuU1@xxxxxxxxxxxxxxxxxx:


"bz" <bz+spr@xxxxxxxxxxxxxxxxxxxx> escreveu na mensagem
news:Xns99F6DA3E1FE47WQAHBGMXSZHVspammote@xxxxxxxxxxxxxxxxx
"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.
Where is the constant torque? The torque is highly variable.

2 - Where does the kinetic energy come from?
The kinetic energy comes from the potential energy.
Since energy is conserved, potential energy needs to be
dissipated. That is, a smaller secondary motion, called
nutation, occurs.

My [not so clear] point was that they mean [to paraphrase slightly] is
that "the precession of mercury is the slow shift of the point of nearest
approach to the sun along the orbital plane," whatever the cause of said
drift.

After taking into account the gravitational effects of all the planets,
there was still some 'precession' left over. They first attributed it to a
small [as yet to be observed] planet inside mercury's orbit, but that
theory was rejected because such an orbit would not be stable.

GR came to the rescue and explained the drift.

So far I'm trying to figure out the problem based on Newton.

When you say, "the precession of mercury is the slow shift of the
point of nearest approach to the sun along the orbital plane" how
does that point shift.
1 - The point becomes closer, or far away, from the sun within
the plane of the orbit.
2 - The distance to the Sun is always the same, but the point
moves in a plane orthogonal of the orbit plane.
(The distance to the Sun is always the same since rotation occurs
along a line that includes the Sun and is orthogonal to the line
defined by the perihelon-sun-aphelion.)


No specific constant 'torque' need be supplied, but the planet 'Vulcan'
would have supplied such a torque if Vulcan existed.

Torque needs to be orthogonal to the plane of the orbit.
That is, the vector torque is in the plane of the orbit.

I guess people say it is precession because they don't know
what precession is and it's a sound name.

Mercury's perihelion advance doesn't look like precession.
Even so, all books and every drawings show a precession
like motion that is constant and requires constant torque.



--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+spr@xxxxxxxxxxxxxxxxxxxx remove ch100-5 to avoid spam trap


.

Relevant Pages

  • Re: Orbital precession w/o GR
    ... of the plane of the orbit (like if the plane of the orbit was ... :>: Precession is due to gyroscopic moment. ... and doesn't give under it if any external torque ... With just two bodies, Sun and Mercury, there would be ...
    (sci.physics.relativity)
  • Re: Orbital precession w/o GR
    ... of the plane of the orbit (like if the plane of the orbit was ... Precession is due to gyroscopic moment. ... and doesn't give under it if any external torque ...
    (sci.physics.relativity)
  • Re: Orbital precession w/o GR
    ... You claim you have measured the perihelion advance. ... the orbit is always the same exact ellipse. ... Actually I cannot see how precession could occur without ... a torque orthogonal to the plane of precession. ...
    (sci.physics.relativity)
  • Re: origin of inertia
    ... Gravity supplies a force of 200 lbf downward on my ... motion on the precession plane. ... Torque = Moment of inertia x dwp/dt ... > no, the angular momentum of the system is conserved, not constant. ...
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  • Re: Orbital precession w/o GR
    ... precession of mercury orbit, ... The rotational motion of the axis of a spinning body, ... See also nutation. ... - Constant precession requires constant torque. ...
    (sci.physics.relativity)