Message-ID: <UZJ0cX-00VcJEFKU4l@andrew.cmu.edu>
Reply-To: space+@Andrew.CMU.EDU
From: space-request+@Andrew.CMU.EDU
To: space+@Andrew.CMU.EDU
Date: Sun,  5 Nov 89 05:23:31 -0500 (EST)
Subject: SPACE Digest V10 #207

SPACE Digest                                     Volume 10 : Issue 207

Today's Topics:
		    Re: Moon Colonies / Ant Tanks?
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Date: 5 Nov 89 05:04:09 GMT
From: mnetor!utzoo!henry@uunet.uu.net  (Henry Spencer)
Subject: Re: Moon Colonies / Ant Tanks?

In article <2723@uceng.UC.EDU> dmocsny@uceng.UC.EDU (daniel mocsny) writes:
>If I haven't botched my handwaving, one result of this is that if the
>earth had a centered spherical void inside it, you would be weightless
>everywhere in that void. Is this correct? ...

This is correct.

>... However, the thinner you made the hollow planet's
>shell, the less weight the shell would have. If the shell were
>infinitely thin, could it have infinite mass without tending to
>collapse?  That can't be right. What am I doing wrong here?

The key issue is the mass.  If you make the shell infinitely thin, it
has zero mass and hence has no tendency to collapse.  If it has nonzero
mass, it needs to have enough strength to resist gravitational collapse.
Collapse is caused by the attraction of the opposite side, and thickness
is (to a first approximation) irrelevant; what matters is strength per
unit mass.
-- 
A bit of tolerance is worth a  |     Henry Spencer at U of Toronto Zoology
megabyte of flaming.           | uunet!attcan!utzoo!henry henry@zoo.toronto.edu

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End of SPACE Digest V10 #207
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