Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!ai.etl.army.mil!hoey
From: hoey@ai.etl.army.mil (Dan Hoey)
Newsgroups: sci.electronics
Subject: Re: Triangular manhole covers (was WHat are those holes for?)
Summary: You *can* put a triangle through a triangular hole
Message-ID: <136@ai.etl.army.mil>
Date: 20 Jul 88 17:43:51 GMT
References: <10790@oberon.USC.EDU> <327@richp1.UUCP> <303@btree.uucp> <1550@tekirl.TEK.COM> <134@ai.etl.army.mil> <4862@killer.DALLAS.TX.US> <624@uhnix2.uh.edu>
Reply-To: hoey@ai.etl.army.mil (Dan Hoey)
Followup-To: sci.math
Organization: Naval Research Lab, Washington, DC
Lines: 27

In article <624@uhnix2.uh.edu> uace0@uhnix2.uh.edu (Michael B. Vederman)
writes:

>Actually, If you don't know, it's because any other shape would either
>be too much of a waste of area (such as a triangle) or the lid would be
>able to fall through the hole and down into the bowels of the city!

In article <4862@killer.DALLAS.TX.US> ltf@killer.DALLAS.TX.US (Lance Franklin)
writes:

>...a equilateral triangle for a manhole cover wouldn't
>fall into the hole either.

And in article <134@ai.etl.army.mil> richr@ai.etl.army.mil (Richard Rosenthal)
writes:

>Triangular (3 sided) covers cannot fall through the hole.

But in fact you *can* slide an equilateral triangle through a hole of the same
shape and slightly smaller size.  You turn it sixty degrees and slide it
through at the base of the hole.  It works because the altitude of the triangle
is less than the side.

You can fudge it by making the cover thick enough, or making the ledge wider.
You can fudge it with a square cover too--just make the cover in the shape of a
cube.

Dan