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#3374 - 09/19/05 06:59 PM Newton's Gravity
jjw Offline
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Registered: 09/07/05
Posts: 636
Loc: USA
In science it is possible to get the wrong perception of the subject matter. For a long time I thought that Newton's laws concerning gravity meant that all items of mass exerted a mutual attraction. While I was working on a project of my own I learned that there is a quirk to this because the positions of the planets in the solar system has not one thing- nada, to do with the mass or the attraction of any of the planets.

The concept that the planets are "falling" into the sun but restrained by orbital momentum is the explanation for what we see. The apparent lack of a contribution of the planets gravity, I think, is explained by "all things fall at the same speed in a vacume" OK. But with that assumption what happens to the basic attraction the planet Earth, or Jupiter, should have for the sun?

I know one of you will have answer for me.
Jim Wood
This seems to imply.

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#3375 - 09/19/05 07:16 PM Re: Newton's Gravity
Uncle Al Offline
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Registered: 10/17/04
Posts: 540
Loc: Southern California
Quote:
I learned that there is a quirk to this because the positions of the planets in the solar system has not one thing- nada, to do with the mass or the attraction of any of the planets.
Aside from relativistic corrections to Newton - sub-part-per-million corrections even in the most extreme cases - you are horribly incorrect. Spacecraft navigation through the solar system is all about multiple-body gravitation effects. There are some remarkably elegant and efficient drift paths. They are among the very few things NASA does very well.

"Gravitation" is the proper word. "Gravity" is gravitation plus centripetal force on the spinning Earth.

Everything orbits barycenters. Discrete analysis all comes out in the general wash. Consider lunar laser ranging and the (never observed) Nordvedt effect,

http://arXiv.org/abs/gr-qc/0411113
<http://www.npl.washington.edu/eotwash/pdf/prl83-3585.pdf>
http://arXiv.org/abs/gr-qc/0301024
Phys. Rev. Lett. 93 261101 (2004)
Nordtvedt Effect
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http://www.mazepath.com/uncleal/qz3.pdf

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#3376 - 09/20/05 09:48 PM Re: Newton's Gravity
jjw Offline
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Registered: 09/07/05
Posts: 636
Loc: USA
Thank you Uncle Al for you comments:
I was gone yesterday and could not acknowledge your reply

We tend to see what we recognize first until we may read again. I think a quirk is not an error. Newton?s work is still supreme with me. I am thinking in terms of Mass like Jupiter being about 313 times that of Earths and looking for some manifestation of that difference in relationship to the Sun.

Note at http://www.spof.gsfc.nasa.gov/stargaze/Sgravity.htm (2/11/2005)

On page two about 2/3rds of the way down the page they recite:

?(Please note: gravity is not what gives the moon its velocity. Whatever velocity the moon has was probably acquired when it (moon) was created. But gravity prevents the moon from running away, and confines it to some orbit.)?

You may tell them the word is ?gravitation?, or not as you may desire.

We are well aware of the interplay between solar objects and that Newton?s work was the breakthrough in those determinations. BUT we have the most massive planet revolving around the sun with little velocity when compare to the Earth, for example. My ?quirk? was aimed at the apparent lack of proof that large massive objects are imparting any extra energy or force to the every day mechanics of this Solar System based on what we know of Newton?s Laws of Gravity.

Read it any way you wish. It is all in fun.
Jim Wood, jjw004

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#3377 - 09/20/05 11:27 PM Re: Newton's Gravity
Uncle Al Offline
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Registered: 10/17/04
Posts: 540
Loc: Southern California
Quote:
My ?quirk? was aimed at the apparent lack of proof that large massive objects are imparting any extra energy or force to the every day mechanics of this Solar System based on what we know of Newton?s Laws of Gravity.
Some asteroid orbits are in small integer resonance with Jupiter's. Ditto near-Earth bodies. Stuff like that. It's there.
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http://www.mazepath.com/uncleal/
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http://www.mazepath.com/uncleal/qz3.pdf

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