Path: utzoo!utgpu!water!watmath!clyde!att!pacbell!ames!think!bloom-beacon!mit-eddie!uw-beaver!tektronix!tekgen!steves
From: steves@tekgen.BV.TEK.COM (Steve Shellans)
Newsgroups: sci.electronics
Subject: Re: Round Manhole Covers (Was: WHat are those holes for?)
Message-ID: <3269@tekgen.BV.TEK.COM>
Date: 21 Jul 88 20:34:04 GMT
References: <10790@oberon.USC.EDU> <327@richp1.UUCP> <303@btree.uucp> <1550@tekirl.TEK.COM>
Reply-To: steves@tekgen.BV.TEK.COM (Steve Shellans)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 16

In article <1550@tekirl.TEK.COM> jackg@tekirl.TEK.COM (Jack Gjovaag) writes:
>In article <303@btree.uucp> rfarris@btree.UCSD.EDU (rick farris) writes:
>>
>>Yes, and why the heck are manholes round?
>
>Aha! I know the answer to this one, even though it has nothing to
>do with electronics.  Round is the only shape for the cover that
>guarantees that the cover can't fall into the hole.  What do I win?

You win a free plane geometry textbook.  Three-cusp hypocycloids have the
same property.  Although they are not round, they have a constant
diameter when measured at any angle of rotation.

Steve Shellans
Tektronix, Beaverton OR
tektronix!tekgen!steves