Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!nrl-cmf!mailrus!uwmcsd1!lakesys!tomk
From: tomk@lakesys.UUCP (Tom Kopp)
Newsgroups: sci.electronics
Subject: Re: WHat are those holes for?
Summary: Manholes
Message-ID: <845@lakesys.UUCP>
Date: 20 Jul 88 02:10:28 GMT
References: <10790@oberon.USC.EDU> <327@richp1.UUCP> <303@btree.uucp>
Organization: Lake Systems, Milwaukee Wisconsin
Lines: 31

In article <303@btree.uucp>, rfarris@btree.uucp (rick farris) writes:
> 
> Yes, and why the heck are manholes round?

Correct me if I'm wrong, but I believe the reason manholes are round is
because it is impossible for a manhole cover to be pushed through the manhole,
even though the actual hole is only minimally 'smaller' due to the rim than
the cover.  No matter how you turn it, a circle still has the same radius.
Picture a square manhole, if you will.  Each side being 2 feet in length (just
for the purpose of this discussion).  each side of the manhole is the same
length, as is (of course) and measurment taken parallel to any side.  However,
between opposite corners, A and C below:
                   A-----B
                   |     |
                   |     |
                   D-----C
The distance is the square root of 8 by pythagorean theorem (sum of the
squares of A-D and D-C equals the square of A-C) which is >2.  Thus, if you
were to first rotate it on the A-D axis so that it were perpendicular to the
ground, With B-C as the top and A-D as the bottom, then rotated it upon the
A-B axis 45 degrees counter-clockwise (as seen from above) You could drop the
cover straight through, as you would be putting an object of length 2ft
through an opening of length (sqrt(8))....They don't want people dropping
covers through the holes as they're quite heavy.
This has been rather verbose, but I don't care.  So sue me.
 

-- 
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