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From: jerry.friedman99@gmail.com (jerryfriedman)
Newsgroups: alt.usage.english,sci.physics
Subject: Re: The antics of thermodynamics, the depravity of relativity, the bunkum
 of quantum
Date: Tue, 11 Mar 2025 14:56:08 +0000
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On Tue, 11 Mar 2025 11:47:06 +0000, Snidely wrote:

> Peter Moylan blurted out:
>> On 11/03/25 15:05, Snidely wrote:
>>> Thus spake Peter Moylan:
>>>
>>>> At the centre of the earth, you also have to taken into account the
>>>> radially directed non-gravitational  force that comes from the
>>>> weight of all the rocks (and so on) above your head.
>>>
>>> Say what?  "non-graviational" from "weight"?
>>
>> Perhaps I should have phrased that better. Consider a hypothetical cave
>> explorer at a distance r from the centre of the earth. The gravitational
>> force experienced by that person, i.e. that person's weight, is that due
>> to the sphere of radius r below him. The gravitational attraction
>> between the person and the earth is not affected by that part of the
>> earth at greater radii.
>
> No, because the gravitational attraction between the person and the
> earth is the /vector/ sum of the attraction between each part of the
> person and each part of the earth, and some of those parts of the earth
> are in the opposite direction of the ones below the person (and many of
> in oblique direction).
...

Peter's right.  What cancels are the forces on the
person from all parts of the Earth at greater radii
than the person.  The weight of the person is due
only to the part of the Earth whose distance from
the center is less than the person's.

This is much more easily proved by Gauss's Law
(which applies to gravitation as well as to
electrostatids) than by integrating those force
vectors.

--
Jerry Friedman

--