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Topic: WHY R MANHOLES ROUND (Read 37201 times) |
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a_noctor
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WHY R MANHOLES ROUND
« on: Nov 21st, 2002, 4:12am » |
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john
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An octagon?
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Graham
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Yes this isn't strictly true - an equilateral triangle won't fall through either...
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James Fingas
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Re: WHY R MANHOLES ROUND
« Reply #4 on: Feb 18th, 2003, 7:54am » |
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Graham,
An equilateral triangle could fall through. Notice how the height of the triangle is smaller than its base, so turn the cover so the height fits into the base of the hole. Whoops!
There are other shapes that wouldn't fall, however: the shapes of constant width. The circle is the simplest of these shapes.
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Doc, I'm addicted to advice! What should I do?
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ShivaM
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Re: WHY R MANHOLES ROUND
« Reply #5 on: Feb 19th, 2003, 8:17am » |
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If the cover is round then is easier to move it by rolling it on the ground.....
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Grimbal
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Re: WHY R MANHOLES ROUND
« Reply #6 on: May 1st, 2004, 9:18am » |
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I would ask: why not? Round is the simplest and most common shape for a hole. Do you think a square hole would be more useful? Wells are round also, even though they don't have a cover.
Regarding what shape does not fall in its own hole, a Y-shaped hole, with 3 branches of the same length and angles 120° would also be safe from falling if the branches are thin enough. Of course, we should consider only convex shapes.
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Dagny
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Re: WHY R MANHOLES ROUND
« Reply #7 on: Oct 7th, 2006, 11:34am » |
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Round cover wud be safer too. It wont hav corners n thus tere r less chances of getting hurt while manipulating the cover.
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irrational
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Re: WHY R MANHOLES ROUND
« Reply #8 on: Nov 1st, 2006, 8:19am » |
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Another reason is:
for a given area, circle has the least perimeter and hence would take the least space.
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Whiskey Tango Foxtrot
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Re: WHY R MANHOLES ROUND
« Reply #9 on: Nov 1st, 2006, 6:19pm » |
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Or that it is the easiest to manufacture.
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"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use." - Galileo Galilei
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Grimbal
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Re: WHY R MANHOLES ROUND
« Reply #10 on: Nov 2nd, 2006, 7:01am » |
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The standard answer is:
- It is the only shape (so they say) that prevents the cover to fall in the hole.
- It is easier to move around, by rolling.
- It is easier to put back because it can be put in any direction.
Here is a picture of a manhole cover near my place note that it is in 2 parts and is on hinges.
Let's see:
- Does the shape prevent the cover to fall in the hole?
- No, it is the hinges.
- Is it easy to move around?
- No. It is round but it cannot be moved around.
- Does the shape make it easier to close?
- No, it's the hinges.
- Is it round?
- Yes
- WHY?
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TenaliRaman
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Re: WHY R MANHOLES ROUND
« Reply #11 on: Nov 15th, 2006, 10:31am » |
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on Nov 2nd, 2006, 7:01am, Grimbal wrote:
- Is it round?
- Yes
- WHY?
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It looks pretty, i wish i could have one too!
-- AI
P.S -> This answer wont get you the job.
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Self discovery comes when a man measures himself against an obstacle - Antoine de Saint Exupery
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BNC
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Re: WHY R MANHOLES ROUND
« Reply #12 on: Nov 21st, 2006, 4:15am » |
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on Nov 2nd, 2006, 7:01am, Grimbal wrote:
- Is it round?
- Yes
- WHY?
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It may be worth repeating what our lost mate Kozo said in the other thread:
on Aug 6th, 2002, 4:45pm, Kozo Morimoto wrote:| According to a civil engineer friend who actually designs the damn things, the dropping theory is pretty cool, but the main reason is probably to do with the same reason why portholes on ships are round - to distribute the load stress evenly and avoid stress points. When you have heavy loads (ie trucks and buses on roads driving over manholes constantly) having 'pointy' shapes would reduce the life of the manholes and increase maintenance requirements. If the dropping thing is correct, why don't they just attach the covers with cables/hinges or make them slide across rather than be able to completely remove them? |
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I also like the (made up) interview with Richard Feynman :
Quote: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. |
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How about supercalifragilisticexpialidociouspuzzler [Towr, 2007]
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Grimbal
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Re: WHY R MANHOLES ROUND
« Reply #13 on: Nov 21st, 2006, 4:34am » |
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Manhole round because mandick round. 
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balanagireddy.tcs
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Re: WHY R MANHOLES ROUND
« Reply #14 on: Nov 25th, 2006, 2:11am » |
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I found a reason why manhole is round...
Basically manholes can be of any shape.
But we need to find something to minimize the area because iron is not that cheap.
and circle is the best possible shape.
Many more shapes like equilateral triangle etc...are also possible.
the reason for manhole is to avoid things fall into those holes.
thats why again circle is the best.
MAN HOLES SHAPE SHOULD BE THE SHAPE OF THE HEAD TOP VIEW.
In future if cubical faces exist...then there will be square manholes...
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checker
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Re: WHY R MANHOLES ROUND
« Reply #15 on: Nov 25th, 2006, 2:30am » |
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I am really surprised to know that such a simple question could be a problem.......When I was asked this in my school days that time I would have found Bala right...but for today Kozo is having the right approach....Well for me every common thing carries a lot of uncommoness.
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| « Last Edit: Nov 25th, 2006, 3:17am by checker » |
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srn437
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Re: WHY R MANHOLES ROUND
« Reply #16 on: Sep 8th, 2007, 8:43pm » |
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Because if they were square(or some other shape) it would be harder to explain why it is.
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Grimbal
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Re: WHY R MANHOLES ROUND
« Reply #17 on: Sep 9th, 2007, 10:26am » |
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I have to make a picture, But I have seen triangular ones!
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JiNbOtAk
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Re: WHY R MANHOLES ROUND
« Reply #18 on: Oct 5th, 2007, 6:56pm » |
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I hate to break it to you guys, but most ( if not all ) of the manholes here in Malaysia is rectangular. In fact, round manholes kinda like endangered species - you know they exist, but its really hard to spot one.
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thunder
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Re: WHY R MANHOLES ROUND
« Reply #19 on: Oct 27th, 2007, 2:46am » |
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since for given dimensions circle has maximum area and
pressure=force/area
hence area being maximum reduces the pressure n th8s possibly the reason behind manholes being round..
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spazdor
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Re: WHY R MANHOLES ROUND
« Reply #20 on: Nov 5th, 2007, 8:59pm » |
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Actually there's lots of shapes that won't fall in.
Probably the simplest such shape (other than the circle) is constructed as follows:
Construct equilateral triangle ABC.
Draw circular arc AB about center C.
Draw circular arc AC about center B.
Draw circular arc BC about center A.
The shape outlined by those three arcs also won't fall down a manhole.
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JiNbOtAk
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Re: WHY R MANHOLES ROUND
« Reply #22 on: Dec 17th, 2007, 4:24am » |
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on Oct 5th, 2007, 6:56pm, JiNbOtAk wrote:| I hate to break it to you guys, but most ( if not all ) of the manholes here in Malaysia is rectangular. In fact, round manholes kinda like endangered species - you know they exist, but its really hard to spot one. |
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Sorry guys, I made an error. According to my wife, the round manholes are for electrical and phone lines. The rectangular ones are for sewage. I guess I'm so used to see the rectangular manhole covers, I kinda blank out on the round ones.
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Random Lack of Squiggily Lines
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Re: WHY R MANHOLES ROUND
« Reply #23 on: Dec 19th, 2007, 1:19pm » |
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wouldn't a triangle be kinda hard to get through, unlike a circle
(at small sizes)
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You can only believe i what you can prove, and since you have nothing proven to cmpare to, you can believe in nothing.
I have ~50 posts to hack a "R" into a "D". Which one?
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Grimbal
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Re: WHY R MANHOLES ROUND
« Reply #24 on: Dec 20th, 2007, 6:50am » |
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hard, but not impossible.
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