So Just Why *Are* Manhole Covers Round?

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Why won't a round cover fall in the hole? Seams to me it would unless the circumference of hole is less than that of cover.

I was asked that today in an interview....lol

A round manhole cover would not fall through its circular opening????

Manhole covers are round simply because the friggen manholes are round. Why would you make a cover different from the opening?

Because they are not square.............

Because round seals in moisture and hence the smell better, than straight edges. The edges would not seal as much during expansion and contraction. Ever wonder why tumblers and dive watches (mostly) are round too? That's why.

A round manhole cover will not fall through a round manhole because the actual circumference of the frame it sits in is slightly greater than the circumference of the whole itself, thus allowing it to lay flush with the street without falling into the whole. No matter how you position the cover, its smallest diameter (all diameters) is larger than any diameter of the hole.

I too, knew the answer would be simple...because holes are round....more specifically manholes are round...does that mean I'm simple???/

Well, I never really thought of that until I read it.

But it totally makes sense, ok round the cover is larger than the opening! So it can't fall in, even if you rotate it or turn it on it's side.

But... If you use a rectangle for example, still the same effect, but if you turn it on it's side or rotate it, it could fall in, or not line up.

Other "Ideas" around the Manhole.

[Content copied from Wikipedia removed.]

many of the above answers are true and correct when they are brought together. yes the hole is round and yes the seal is better and yes it cannot fall into the hole. there are other factors too, such as a circle being the strongest shape therefore alowing maximum strength and being able to cope with the huge volume of weight and pressure from above the street. the portability aspect of being able to manouvre the cover due to its rondness is also true. therefore manhole covers MUST be round!!!! and no i did not miss the point of the question

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