[Guest]

Why are sewer lids circular?

Because a circle is the only geometric shape that, barring any physical changes, cannot fall through a hole with equal circumference. Think of square or triangle, you can turn them diagonally to the hole. With any polygon that might be reasonable to use for sewer lids, it could be manipulated to fall through the hole.

[fabpig]

see here

Edited March 7, 2011 by fabpig

[superprismatic]

and so does his Reuleaux triangle!

[Guest]

Because the sewer hole is round! Any other shape lid would not fit.

[Guest]

Upper edge is wider that bottom edge of the ring the sit on.

[Smith]

I thought it was interesting that this "riddle" involved the word "sewer" rather than asking "why are manhole covers circular". The reason I find it interesting is because of the wording of the quote in my sig, but maybe it is a regional thing. I'm from the Los Angeles area, and Mel Brooks is from Brooklyn. Now I wonder where ace_pubchat is from?

[Guest]

so you can roll them across the ground to get them from place to place, since they're so heavy. You can't do that with a Reuleaux triangle!

[Guest]

I suppose it would have been better if I would have included in my answer that the circular lids also fit in any orientation, as opposed to the Reuleaux triangle which would require the edges and corners be aligned.

[Guest]

Oh, and Smith, I am 60 little miles away from you in San Bernardino. I just worded the question as it was given to me. When I took critical thinking in college my professor offered that anyone who could answer a logic question correctly could not show up for the term and get an A. It was this question. Three people tried to answer before me, but I got it right first. I always liked the question, even if the original answer no longer holds true.

[Aaryan]

Posted already

[Guest]

My apologies. I searched for sewer lids not manhole covers.