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  4. Does Newton's shell theorem account for tidal forces?
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Does Newton's shell theorem account for tidal forces?

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Offline cowlinator (OP)

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Does Newton's shell theorem account for tidal forces?
« on: 17/12/2016 20:30:50 »
Does Newton's shell theorem account for tidal forces?

If so, wouldn't all spherically symmetric bodies of mass be gravitationally identical to a singularity of the same mass, to an outside observer?
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Offline yor_on

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Re: Does Newton's shell theorem account for tidal forces?
« Reply #1 on: 17/12/2016 20:44:44 »
Not as I see?
http://teacher.pas.rochester.edu/PHY235/LectureNotes/Chapter05/Chapter05.htm

The shell theorem is about static 'point masses' that can be reduced to a point at a center.
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I guess Pete is the one that would give the best answer there.
« Last Edit: 17/12/2016 20:49:34 by yor_on »
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Offline chris

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Re: Does Newton's shell theorem account for tidal forces?
« Reply #2 on: 18/12/2016 00:38:33 »
Forgive my ignorance, but what is Newton's Shell Theorem?
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Re: Does Newton's shell theorem account for tidal forces?
« Reply #3 on: 18/12/2016 06:34:39 »
Quote from: chris on 18/12/2016 00:38:33
Forgive my ignorance, but what is Newton's Shell Theorem?
A spherically symmetric body affects external objects gravitationally as though all of its mass were concentrated at a point at its centre.
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Re: Does Newton's shell theorem account for tidal forces?
« Reply #4 on: 18/12/2016 12:19:24 »
Newton’s Shell Theorem 
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Offline rmolnav

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Re: Does Newton's shell theorem account for tidal forces?
« Reply #5 on: 20/12/2016 11:25:31 »
Does Newton's shell theorem account for tidal forces?
It could be said that it is quite the OPPOSITE.
C.G. of objects are kind of abstract tools, useful when dealing with problems related to ADDED gravitational effects on objects, no matter how material, real particle masses are distributed across the objects.
But distance from Moon to different Earth´s points are varies a lot, and subsequently so does Moon´s pull (the further the smaller pull).
And required centripetal force at those points (to produce the rotation around Moon/Earth barycenter, all particles at same angular speed) varies too (the further the bigger required centripetal force).
Those two facts mean there is an imbalance that, as far as I can understand, only can be compensated by internal stresses/forces, which are the cause of sea tides. They also produce deformations where Earth solid material.
This issue has been long discussed on:
http://www.thenakedscientists.com/forum/index.php?topic=49715.new#lastPost
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Re: Does Newton's shell theorem account for tidal forces?
« Reply #6 on: 28/12/2016 06:09:07 »
Quote from: cowlinator on 17/12/2016 20:30:50
Does Newton's shell theorem account for tidal forces?

If so, wouldn't all spherically symmetric bodies of mass be gravitationally identical to a singularity of the same mass, to an outside observer?
The answer to both of your questions is yes.
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Offline yor_on

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Re: Does Newton's shell theorem account for tidal forces?
« Reply #7 on: 02/01/2017 09:21:25 »
Heh, should have read the whole link I gave there. But it seemed quite obvious to me that Newton wouldn't have considered tidal forces. But I was wrooonnng :) The mathematics was good enough to allow for tidal forces too it seems.
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II shall hereby atone for my mistake with a humble offering to the Gods, and anyone interested :)

Isaac Newton and the Laws of Motion and Gravitation 1 
Isaac Newton and the Laws of Motion and Gravitation 2 
« Last Edit: 02/01/2017 09:37:17 by yor_on »
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