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Subject: Do you know why manhole covers (and, by extention manholes) are round? rss

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¡dn ʇǝƃ ʇ,uɐɔ ı puɐ uǝllɐɟ ǝʌ,ı
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1) A round manhole cover has less area than a square of the same size, and it therefore weighs less. Considering your round cover weighs a lot on its own, you'll be glad for whatever extra weight that you have to avoid lifting.

2) More importantly, if you rotate a square cover-- you can prove this using simple geometry (Pythagoras)-- then the distance from corner to corner (across the center) of the slightly smaller square "hole" is still greater than the length of each of the sides of the square.
If you move things incorrectly, and your (heavier) square manhole cover is going to fall through the hole, someone has to bring it up again.

A round cover cannot fall through a slightly smaller round hole.

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Matt
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MABBY wrote:
1) A round manhole cover has less area than a square of the same size, and it therefore weighs less. Considering your round cover weighs a lot on its own, you'll be glad for whatever extra weight that you have to avoid lifting.

2) More importantly, if you rotate a square cover-- you can prove this using simple geometry (Pythagoras)-- then the distance from corner to corner (across the center) of the slightly smaller square "hole" is still greater than the length of each of the sides of the square.
If you move things incorrectly, and your (heavier) square manhole cover is going to fall through the hole, someone has to bring it up again.

A round cover cannot fall through a slightly smaller round hole.



Although fascinating, this is not quite true... The original designs under consideration were square and triangle, but they couldn't decide, so they flipped a coin.

As the coin was tumbling in its parabola, the lead engineer grabbed it out of the air and said, "Oh! Never mind, got it." He grabbed the coin and left to hurriedly redesign the cover.

The project was three weeks late, but most customers were pretty happy with the design.

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Rusty McFisticuffs
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MABBY wrote:
2) More importantly, if you rotate a square cover-- you can prove this using simple geometry (Pythagoras)-- then the distance from corner to corner (across the center) of the slightly smaller square "hole" is still greater than the length of each of the sides of the square.
If you move things incorrectly, and your (heavier) square manhole cover is going to fall through the hole, someone has to bring it up again.

A round cover cannot fall through a slightly smaller round hole.

Neither can a triangle, which means the most important reason is that round covers are easier to roll.
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Terry Kirk
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In the UK we have a mix.
About half round, and half triangle.

I assumed it's so they can't fall in.
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Boaty McBoatface
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kirkatronics wrote:
In the UK we have a mix.
About half round, and half triangle.

I assumed it's so they can't fall in.
I have seen square ones too.
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Erik Henry
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Because alligators are square in cross-section and can't fit through a round hole--and obviously you wouldn't want them crawling up out of the sewers.
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Terry Kirk
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slatersteven wrote:
kirkatronics wrote:
In the UK we have a mix.
About half round, and half triangle.

I assumed it's so they can't fall in.
I have seen square ones too.

I've seen the square ones too, but they're usually 2 triangles. Where I am anyway.
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Mark O'Reilly
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By definition a man hole is round
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John Breckenridge
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Why does the cover have to be the same shape as the hole? A square cover over a round hole isn't going to fall in either.
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Barry Harvey
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Too long has the manhole cover world been dominated by round covers (and also square covers in Britain). Maybe there should be more diversity.

Of course
I'm going to say hexagonal covers. Six sides best.
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Maui Chris
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biffta wrote:
By definition a man hole is round


challenge accepted...

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Andy Andersen
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"You're gonna need a bigger manhole cover"
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David Bush
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kuhrusty wrote:
MABBY wrote:
2)

A round cover cannot fall through a slightly smaller round hole.

Neither can a triangle, which means the most important reason is that round covers are easier to roll.

If the three sides of a triangular hole are more than 90% of the length of the sides of the cover, the cover could fall through the hole. I was surprised to find images of such manholes anyway. If the sides are bowed out so that the distance to the opposite vertex is constant, which is called a Reuleaux triangle, then it cannot fall through. Apparently it also works if the sides are bowed in.

This could be done with any odd number N of points, not just 3, although the higher the value of N, the more the object looks like a circle.
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Joe Salamone
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My toilet seat is round, but I keep falling in.
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¡dn ʇǝƃ ʇ,uɐɔ ı puɐ uǝllɐɟ ǝʌ,ı
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caracfergus wrote:
Too long has the manhole cover world been dominated by round covers (and also square covers in Britain). Maybe there should be more diversity.

Of course
I'm going to say hexagonal covers. Six sides best.


I thought you were going to suggest the more PC, "Personhole", and "Personhole cover".
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I have clearly been away from chit chat for too long. I am crying with laughter. My husband is very happy with you all right now.
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Robert Wesley
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wow ONE 'shape' not in 'consideration' was that:

robot ~itsblankablanktrapezoid
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Bryan Thunkd
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It's called a manhole cover and I've never seen a man with a square belly! It makes sense that if you want to make something a man can fit into, you'd make it just slightly larger than belly sized.
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Robert Wesley
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MABBY wrote:
I thought you were going to suggest the more PC, "Personhole", and "Personhole cover".
Where WERE this OTHER "supposed"-'gender person' whence the MAN "descended unto" there? shake
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Celina
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GROGnads wrote:
MABBY wrote:
I thought you were going to suggest the more PC, "Personhole", and "Personhole cover".
Where WERE this OTHER "supposed"-'gender person' whence the MAN "descended unto" there? shake




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Tom Patterson
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What were you expecting?
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Well, I've played many games of Mr. Jack and I just sort of assume they're all hexagonal.
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Adrian Hague
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I'd like to talk about gender equality and the place of the ladyhole in society, but I think it would send this thread straight to RSP.
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Dennis Ku
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None of this is true. The real reason they're round is because they're easier to throw. Have you ever tried throwing a square manhole cover? Impossible.
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Agent J
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He's looking real sharp in his 1940's fedora. He's got nerves of steel, an iron will, and several other metal-themed attributes. His fur is water tight and he's always up for a fight.
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futhee wrote:
None of this is true. The real reason they're round is because they're easier to throw. Have you ever tried throwing a square manhole cover? Impossible.


TMNT reference?
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Mike Norris
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AdrianPHague wrote:
I'd like to talk about gender equality and the place of the ladyhole in society, but I think it would send this thread straight to RSP.


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