Darren New wrote:
> Actually, I've never seen anyone get the answer write to "why are 
> manholes round."  I almost hope they ask me that at my next job 
> interview, because the interviewer probably doesn't know either. ;-)

It's because the subterranean creatures that burrow around make *round* 
holes when they surface.  Silly.

-- 
Tim Cook
http://empyrean.digitalartsuk.com

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Slime wrote:
> I learned the answer from an Encyclopedia Brown book when I was a kid.

Really?? What did he think the answer was?

-- 
   Darren New / San Diego, CA, USA (PST)
     "That's pretty. Where's that?"
          "It's the Age of Channelwood."
     "We should go there on vacation some time."

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"Darren New" <dne### [at] sanrrcom> wrote

> Actually, I've never seen anyone get the answer write to "why are

Just hope that they don't ask you to write the answer...

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"somebody" <x### [at] ycom> wrote in message news:484b2fcb@news.povray.org...
> "Darren New" <dne### [at] sanrrcom> wrote

> > Actually, I've never seen anyone get the answer write to "why are

> Just hope that they don't ask you to write the answer...

Which, by the way, is of course "because the covers are round".

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somebody wrote:
>> Just hope that they don't ask you to write the answer...

Yes. Blame the tequila.  (I knew someone would bring that up. :-)

> Which, by the way, is of course "because the covers are round".

Nope.

-- 
   Darren New / San Diego, CA, USA (PST)
     "That's pretty. Where's that?"
          "It's the Age of Channelwood."
     "We should go there on vacation some time."

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Darren New wrote:
> Actually, I've never seen anyone get the answer write to "why are 
> manholes round."  I almost hope they ask me that at my next job 
> interview, because the interviewer probably doesn't know either. ;-)

	I like the fake Feynman answer:

START

Interviewer: Now comes the part of the interview where we ask a question 
to test your creative thinking ability. Don't think too hard about it, 
just apply everyday common sense, and describe your reasoning process.

Here's the question: Why are manhole covers round?

Feynman: They're not. Some manhole covers are square. It's true that 
there are SOME round ones, but I've seen square ones, and rectangular ones.

Interviewer: But just considering the round ones, why are they round?

Feynman: If we are just considering the round ones, then they are round 
by definition. That statement is a tautology.

Interviewer: I mean, why are there round ones at all? Is there some 
particular value to having round ones?

Feynman: Yes. Round covers are used when the hole they are covering up 
is also round. It's simplest to cover a round hole with a round cover.

Interviewer: Can you think of a property of round covers that gives them 
an advantage over square ones?

Feynman: We have to look at what is under the cover to answer that 
question. The hole below the cover is round because a cylinder is the 
strongest shape against the compression of the earth around it. Also, 
the term "manhole" implies a passage big enough for a man, and a human 
being climbing down a ladder is roughly circular in cross-section. So a 
cylindrical pipe is the natural shape for manholes. The covers are 
simply the shape needed to cover up a cylinder.

Interviewer: Do you believe there is a safety issue? I mean, couldn't 
square covers fall into the hole and hurt someone?

Feynman: Not likely. Square covers are sometimes used on prefabricated 
vaults where the access passage is also square. The cover is larger than 
the passage, and sits on a ledge that supports it along the entire 
perimeter. The covers are usually made of solid metal and are very 
heavy. Let's assume a two-foot square opening and a ledge width of 1-1/2 
inches. In order to get it to fall in, you would have to lift one side 
of the cover, then rotate it 30 degrees so that the cover would clear 
the ledge, and then tilt the cover up nearly 45 degrees from horizontal 
before the center of gravity would shift enough for it to fall in. Yes, 
it's possible, but very unlikely. The people authorized to open manhole 
covers could easily be trained to do it safely. Applying common 
engineering sense, the shape of a manhole cover is entirely determined 
by the shape of the opening it is intended to cover.

Interviewer (troubled): Excuse me a moment; I have to discuss something 
with my management team. (Leaves room.)

(Interviewer returns after 10 minutes)

Interviewer: We are going to recommend you for immediate hiring into the 
marketing department.

END

Taken from:

http://www.sellsbrothers.com/fun/msiview/#Feynman

I have to strongly agree with one point - why do people keep thinking 
they are just round? I've seen *many* square shaped ones.

-- 
Copywight 1991 Elmer Fudd.  All wights wesewved


                     /\  /\               /\  /
                    /  \/  \ u e e n     /  \/  a w a z
                        >>>>>>mue### [at] nawazorg<<<<<<
                                    anl

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> Really?? What did he think the answer was?

Just so they can't fall in.

 - Slime
 [ http://www.slimeland.com/ ]

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Darren New wrote:
> Actually, I've never seen anyone get the answer write to "why are 
> manholes round."  I almost hope they ask me that at my next job 
> interview, because the interviewer probably doesn't know either. ;-)
> 

You know, I had to check what a "manhole" actually is - and I waited for 
some seriously wrong answers from Google, but the first answers actually 
covered my actual question.

-- 
Eero "Aero" Ahonen
    http://www.zbxt.net
       aer### [at] removethiszbxtnetinvalid

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Darren New wrote:
> Actually, I've never seen anyone get the answer write to "why are 
> manholes round."  I almost hope they ask me that at my next job 
> interview, because the interviewer probably doesn't know either. ;-)

The snarky answer is "because manhole covers around round" is the 
punchline of a joke, but does not answer the serious question at hand.

A manhole is *circular* minimize the amount of extra material needed to 
make it impossible for the cover to fall into the manhole.

The manhole has a certain radius.  The manhole cover has a slightly 
higher radius.  In every direction, the diameter of the cover is larger 
than the diameter of the hole, taken in any direction.  This is 
accomplished if the cover's radius is even a millimeter larger, although 
to allow for wear and the thermal expansion of the hole or contraction 
of the cover, a larger difference--no more than a centimeter--is prudent.

With any other shape, the required amount to ensure non-falling-in 
behavior is larger.  A square, or a pentagon, or any n-gon, is larger 
from corner to opposing corner (or most opposing corner for n-gons with 
an odd number of vertices) than from side to opposing side (or corner to 
opposing side).  If the difference is larger than the extra amount added 
on to make the cover bigger than the hole, the lid falls in, and so the 
extra amount would need to be larger.

Minimizing the extra material is important because manhole covers are 
heavy; adding to the radius greatly increases the weight of the cover, 
because the weight is proportional to the area times the thickness. 
Area is proportional to the square of the radius.  As any programmer can 
tell you, when faced with an O(n^2) problem that is unavoidable, you 
make n as small as you can.

Also, a circular manhole fits in any direction.  A polygonal manhole 
cover has to be turned to fit, or else be picked up again (these things 
are heavy) or the corners will wear (or break) off after a bunch of 
near-misses.

Regards,
John

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John VanSickle <evi### [at] hotmailcom> wrote:
> A manhole is *circular* minimize the amount of extra material needed to 
> make it impossible for the cover to fall into the manhole.

  Are you sure it's a question of minimizing material and not simply because
it's the *simplest* possible solution for the problem (ie. avoid the cover
to ever fall into the manhole)?

-- 
                                                          - Warp

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