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From: Peter Moylan <peter@pmoylan.org>
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 20:23:15 +1100
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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.

That point is agreed by everyone here.

However there is another relevant force. The roof of the cave is
supporting the weight of the material above it. (And it is a weight, so
I shouldn't have called it non-gravitational. But it's different from
the weight of the cave explorer.) As long as the roof doesn't collapse,
that force doesn't affect the explorer. Go deep enough, though, and that
second weight is big enough so that the roof will indeed collapse, so
our explorer will (very briefly) experience it. Deep underground, the
pressure is so high that no voids can exist. No caves, so no journey to
the centre of the earth.

-- 
Peter Moylan       peter@pmoylan.org    http://www.pmoylan.org
Newcastle, NSW