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To prevent the need for sewer diving being included in utility workers job descriptions.;P
So the cover doesn't slip through the hole.
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Because that is the only shape that is guaranteed not to fall into the hole!
Daniel Bragg
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It's the only shape that won't fall through the hole it covers.
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two reasons, 1 the covers can not fall into the hole, 2 the covers are easy to move, simply flip them on edge and roll them away.
You may be right
I may be crazy
-- Billy Joel --
Within you lies the power for good, use it!!!
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In the UK, most man hole covers are rectangular... We have the problem of round pegs going into square holes in order to do drain repairs...
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'Cause the manholes are? 
š
Cheers,
Vikram.
I don't know and you don't either.
Militant Agnostic
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It is the only goemetric shape which cannot be manipulated to fall back down in the hole.
Jordon
News Editor/Publisher
The Code Project Insider
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Actually, that's not true. There's a class of polygons called Reuleaux Polygons that won't fall back down the hole. The reason a circle won't fall back down the hole is because it has a constant width, it's diameter. The simplest Reuleaux Polygon is the Reuleaux triangle. This shape is formed by starting with an equilateral triangle and drawing three arcs of circles, each having it's center at the corner of the triangle, a radius equal to the length of the side of the triangle, and the endpoints of the arcs being the other two corners of the triangle (like the cross-section of a bottle of Pepto-Bismol or the piston in the Wankel rotary engine). Figure 1.
Because this shape has a constant width (the length of the side of the equilateral triangle) it will not fall through the hole.
You can create this kind of shape from any polygon having an odd number equal-length sides.
So, I suspect that the round manhole cover not falling through the hole is only one reason that the cover is round. Other reasons are probably
1. Round manhole are easier to manufacture.
2. Because the pipe leading to the manhole is round.
3. The round-shaped object is the strongest structurally (that's why submarines are round and not square).
4. A round manhole cover is easier for one person to move by standing it on it's side and rolling it.
5. You don't have to align an manhole cover to it's hole to replace it.
I'm sure there are more reasons, but you get the general idea. The question is not about the answer. It's about your ability to reason.
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A human is least likely to go bald if they have this hair color?
Jordon
News Editor/Publisher
The Code Project Insider
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Blonde - and not from a bottle...
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i cant safely say its not brown. i think i have to agree with blonde.
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By golly gee whizzzz yourboss is one fart smeller...
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I'll say gray (or silver) since if they were going to go bald, they would have already done it by then.
"If you really want something in this life, you have to work for it. Now, quiet! They're about to announce the lottery numbers..."
- Homer Simpson
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Red
Jordon
News Editor/Publisher
The Code Project Insider
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Where were the abandoned 1940 Olympic Games due to be held?
Jordon
News Editor/Publisher
The Code Project Insider
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Berlin???
Oops...it was the other Axis power capital...Tokyo...
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Tokyo, Japan.
I think they were later slated to be held in Helsinki, Finland, but that was cancelled too.
š
Cheers,
Vikram.
I don't know and you don't either.
Militant Agnostic
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Winter: Sapporo, Japan -> St Moritz, Switzerland -> Garmisch-Partenkirchen, Germany -> cancelled
Summer: Tokyo, Japan -> Helsinki, Finland -> cancelled
- Dave
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Again nice work guys. I need to start making these harder
Tokyo, Japan
Jordon
News Editor/Publisher
The Code Project Insider
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Where are the highest cliffs in Europe?
Jordon
News Editor/Publisher
The Code Project Insider
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Slieve League in Ireland, 598 meters.
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