ash asmenishkai pirma pagalvojau apie ridenima :)
"Interested" <z@none.lt> wrote in message 
news:ig19p1$b68$1@trimpas.omnitel.net...
> Ačiū, geros mįslės. Kai kurias net sunku įsivaizduoti, kaip kažkas 
> atspėja. Faktas, kad tikrai ne visi klausimai turi tik vieną teisingą 
> atsakymą.
> --------------------------------------
> Circular shape
> The question of why manhole covers are typically round, at least in the 
> U.S., was made famous by Microsoft when they began asking it as a 
> job-interview question.[6][7][8] Originally meant as a psychological 
> assessment of how one approaches a question with more than one correct 
> answer, the problem has produced a number of alternate explanations, from 
> the pragmatic ("Manhole covers are round because manholes are round.")[6] 
> to the philosophical.
> Reasons for the shape include:
> A round manhole cover cannot fall through its circular opening, whereas a 
> square manhole cover may fall in if it were inserted diagonally in the 
> hole. (A Reuleaux triangle or other curve of constant width would also 
> serve this purpose, but round covers are much easier to manufacture. The 
> existence of a "lip" holding up the lid means that the underlying hole is 
> smaller than the cover, so that other shapes might suffice.)
> Round tubes are the strongest and most material-efficient shape against 
> the compression of the earth around them, and so it is natural that the 
> cover of a round tube assume a circular shape.
> Similarly, it is easier to dig a circular hole and thus the cover is also 
> circular.
> The bearing surfaces of manhole frames and covers are machined to assure 
> flatness and prevent them from becoming dislodged by traffic. Round 
> castings are much easier to machine using a lathe.
> Circular covers do not need to be rotated to align them when covering a 
> circular manhole.
> Human beings have a roughly circular cross-section.
> A round manhole cover can be more easily moved by being rolled.
> If a cover had corners and were bent that would create a protruding point 
> that could puncture tires.
> Most manhole covers are made by a few large companies. A different shape 
> would have to be custom made.
> Other manhole shapes can be found, usually squares or rectangles. Nashua, 
> New Hampshire may be unique in the U.S. for having triangular manhole 
> covers that point in the direction of the underlying flow. The city is 
> phasing out the triangles, which were made by a local foundry, because 
> they are not large enough to meet modern safety standards, and larger 
> triangles cannot be found.[9]
> ---------------------------------------------------------------------------
> http://en.wikipedia.org/wiki/Manhole_cover