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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. ;-)
--
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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I learned the answer from an Encyclopedia Brown book when I was a kid.
- 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. ;-)
It's because the subterranean creatures that burrow around make *round*
holes when they surface. Silly.
--
Tim Cook
http://empyrean.digitalartsuk.com
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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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] san rrcom> 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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"Darren New" <dne### [at] sanrrcom> wrote
> 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.
Wrong you are, but if you want a more verbose answer:
In "space", the natural shape for anything is a sphere (maximal symmetry for
anything finite). On the surface of the earth, gravity breaks symmetry
(vertical axis is different from the others) so spherical symmetry reduces
to cylindrical symmetry. The natural symmetry for *anything* on the surface,
barring any other constraints, is therefore cylindrical. Since there
typically is no good reason (ask not why is X, but why is not not X) to make
manhole covers non-cylindrical, most are cylindrical. Hence the holes.
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somebody wrote:
> typically is no good reason (ask not why is X, but why is not not X) to make
> manhole covers non-cylindrical, most are cylindrical. Hence the holes.
Errr, no. Indeed, if you actually look, most manholes on the *sidewalk*
are not round. And even small "manholes" like for meters and such, as
big as your spread hand, are round when they're in the street.
Chances are you won't just guess unless you've actually ever seen the
outside of a manhole.
Given the hint that they're all round in the street and they're not
round on the sidewalk... any more takers?
(As for the "so it won't fall in the hole" bit, people invented hinges
long before they invented manholes.)
--
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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John VanSickle 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 guessing, or have you actually (say) worked someplace that
designs manholes? :-)
> Minimizing the extra material is important because manhole covers are
> heavy;
Even six-inch wide manhole covers covering holes a foot deep are round.
> 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.
Hinges are your friend. :-)
--
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:
>
> Given the hint that they're all round in the street and they're not
> round on the sidewalk... any more takers?
I can't actually agree on this, but it can depend on the country etc, so
that doesn't matter. There's 2 reasons:
1) No corners -> no tire fatalities.
2) Harder pressure on ground surface (there can be tonnes of masses on
one axle on the street) -> harder construction (cylindrical shape is
better to handle pressure from outside).
--
Eero "Aero" Ahonen
http://www.zbxt.net
aer### [at] removethiszbxtnetinvalid
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On Sun, 08 Jun 2008 08:32:33 -0700, Darren New <dne### [at] sanrrcom>
wrote:
>Hinges are your friend. :-)
I'm not sure what you're thinking about but hinges are not your friend
when your talking about manholes. The manhole cover can be left up.
(Naughty, naughty) Also hinges would be a weak point and liable to
break. They would also involve lifting the heavy manhole cover upright
which would take more effort than lifting it up an inch or two and
sliding it away.
--
Regards
Stephen
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"Darren New" <dne### [at] sanrrcom> wrote in message
news:484b0f3d$1@news.povray.org...
> 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.
> ;-)
>
> --
> 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."
Round manholes fit whichever orientation you drop them.
Round manholes cover (usually) cyclindrical access spaces which are
better able to resist ground pressures and (again) permit putting
thiings
into them without concern for orientation. (Round pegs/square
holes:
square pegs/round holes).
Lots more reasons, but it is a field question as opposed to some
design or theoretical question: what works best and easiest is
what is done.
If you've ever worked with manhole covers you know it is enough
work
without having to fit corners.
(also - odds are any sufficeintly sized circular manhole cover will
fit
the odd hole and the odds are that covers with corners will not
work as a --- cover.)
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"Darren New" <dne### [at] sanrrcom> wrote in message
news:484bfade@news.povray.org...
> somebody wrote:
> > typically is no good reason (ask not why is X, but why is not not X) to
make
> > manhole covers non-cylindrical, most are cylindrical. Hence the holes.
> Errr, no. Indeed, if you actually look, most manholes on the *sidewalk*
> are not round. And even small "manholes" like for meters and such, as
> big as your spread hand, are round when they're in the street.
>
> Chances are you won't just guess unless you've actually ever seen the
> outside of a manhole.
>
> Given the hint that they're all round in the street and they're not
> round on the sidewalk... any more takers?
That's not a given by a long shot. Manholes here and all places I've seen
are round in the sidewalk too. The city isn't going to maintain two
different types of manholes unless there's a good reason (the sidewalk ones
might be thinner, I naturally did not inspect carefully). The large
rectangular ones you see on sidewalks on cities are not manholes but grills.
There are also rectangular storm drains (some are even formed into an S
shape between the road and the sidewalk for accessibility). However, neither
grills nor storm drains are meant for a "man" to go through a "hole", so are
not manholes, nor are the holes in the ground for meters that you mention.
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On Sun, 08 Jun 2008 08:32:33 -0700, Darren New wrote:
>> 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.
>
> Hinges are your friend. :-)
Hinges introduce additional complexity and are subject to breakage under
stress...
Jim
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pan <pan### [at] syixcom> wrote:
> Round manholes fit whichever orientation you drop them.
> Round manholes cover (usually) cyclindrical access spaces which are
> better able to resist ground pressures and (again) permit putting
> thiings
> into them without concern for orientation. (Round pegs/square
> holes:
> square pegs/round holes).
You left out the fact that a round cover will not fall into the manhole
no matter how you might screw up opening it.
--
- Warp
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Warp wrote:
> You left out the fact that a round cover will not fall into the manhole
> no matter how you might screw up opening it.
And what everyone so far has missed is that roads get repaved. The
manhole screws into the vault at the bottom (so you can make it flush
with the surface of the road) and has threads on the outside. When you
repave the road, the first thing you do is give all the manholes an
extra crank or two to lift them up an inch or so, so they stay flush
with the surface of the road after you add more asphalt.
Plus, of course, it takes less metal to make a round cover to cover a
certain opening than any other shape, which is important when you're
planning to place millions of manholes and calculating how much your raw
materials will cost.
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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On Sun, 08 Jun 2008 14:27:26 -0700, Darren New <dne### [at] sanrrcom>
wrote:
>And what everyone so far has missed is that roads get repaved. The
>manhole screws into the vault at the bottom
Not in the UK they don't. They are kept in position by gravity. They
lift in and out vertically.
--
Regards
Stephen
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Stephen wrote:
> Not in the UK they don't. They are kept in position by gravity. They
> lift in and out vertically.
Wow. How do they keep them level with the road, then? How do they even
make them level with the road in the first place?
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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"Darren New" <dne### [at] sanrrcom> wrote
> Warp wrote:
> > You left out the fact that a round cover will not fall into the
manhole
> > no matter how you might screw up opening it.
> And what everyone so far has missed is that roads get repaved. The
> manhole screws into the vault at the bottom (so you can make it flush
> with the surface of the road) and has threads on the outside. When you
> repave the road, the first thing you do is give all the manholes an
> extra crank or two to lift them up an inch or so, so they stay flush
> with the surface of the road after you add more asphalt.
Another incidental benefit, but not the ultimate reason. Manholes have
always been predominantly round, even in cobblestone streets, which are not
designed for repaving higher, and where round bezels are actually often a
*liability* (See
http://images.google.ca/images?hl=en&q=cobblestone%20manhole ). Plus not all
manhole bezels are threaded in.
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Hinged...
http://www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs/images/figure05.jpg
Decorated...
http://barista.media2.org/wp-content/manhole%20japan.jpg
http://www.pinktentacle.com/2007/10/japanese-manhole-covers/
Square...
http://www.tilingandpoolprojects.co.uk/images/manHoleLarge.jpg
http://www.forgotten-ny.com/STREET%20SCENES/manholes/CT&ESC.jpg
http://www.soe.uoguelph.ca/webfiles/wjames/illustrations/AestheticInfrastructure/MHcoverSquareSanitaryPafosCyprus.JPG
http://farm2.static.flickr.com/1320/1431363588_d3de12ea72.jpg?v=0
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somebody wrote:
> Another incidental benefit, but not the ultimate reason. Manholes have
> always been predominantly round, even in cobblestone streets, which are not
> designed for repaving higher,
Well, sure. Are manholes older or newer than paved streets, tho? Once
you have paved streets and decide you need manholes to be round for
them, one might decide that one might as well use manholes on paved
streets, as well?
> http://images.google.ca/images?hl=en&q=cobblestone%20manhole ).
Funny enough, the first image at that link shows a square manhole for
me. :-)
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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And lo on Sun, 08 Jun 2008 23:01:45 +0100, Darren New <dne### [at] sanrrcom>
did spake, saying:
> Stephen wrote:
>> Not in the UK they don't. They are kept in position by gravity. They
>> lift in and out vertically.
>
> Wow. How do they keep them level with the road, then? How do they even
> make them level with the road in the first place?
If you're talking about what I think you are then there are adjustment
bricks that can be altered to raise or lower the level, but on a new road
(or a stripped one) the level of the road surface is dictated by the
ironworks. If an alteration is done then a square is cut around the cover,
the work is done and that section of road is resurfaced to the level of
the ironwork. Oh sure there are rules about the degree of difference
between new and existing surfaces - heh, but this is why we have the lumpy
bumpy roads we know and love :-P
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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On Mon, 09 Jun 2008 09:38:12 +0100, "Phil Cook"
<phi### [at] nospamrocainfreeservecouk> wrote:
>If you're talking about what I think you are
...
Thanks Phil, you said it just as well as I could or better :)
--
Regards
Stephen
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And lo on Mon, 09 Jun 2008 09:50:37 +0100, Stephen <mcavoysAT@aolDOTcom>
did spake, saying:
> On Mon, 09 Jun 2008 09:38:12 +0100, "Phil Cook"
> <phi### [at] nospamrocainfreeservecouk> wrote:
>
>> If you're talking about what I think you are
> ...
>
> Thanks Phil, you said it just as well as I could or better :)
My pleasure. Not that I, you know, take any real interest in road surfaces
:-P
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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On Mon, 09 Jun 2008 09:58:55 +0100, "Phil Cook"
<phi### [at] nospamrocainfreeservecouk> wrote:
>
>My pleasure. Not that I, you know, take any real interest in road surfaces
>:-P
I understand and it has been many years since I inspected gutters
close up :)
--
Regards
Stephen
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Warp wrote:
> 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)?
It is the simplest solution, but if another solution used less material,
economics would drive one of those solutions.
Regards,
John
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