I put the answers up in my first post.

 

I heard the manhole thing was a microsoft question too....

but if it they weren't circles.. think of how many more tax dollars we would have to pay the unions to spend time figuring out why the covers don't fit and how to rotate them .... instead of a round thing that is standardized.. people would prolly find a way to have different dimensions on them, then someone would change them.. and you'd end up with 20 different sized manholes.... good grief

 

I think a "Wankel rotary engine" shaped manhole cover might not fall through either.

 

amen brutha

 

how big is the typical cover? 3 ft? That's a whole hell of a lot of weight needed to cause any real issue considering the material a manhole is made out of. It's not like people go around town in vehicles that could cause any damage to a square one. Oh that's right some manhole covers are square anyways, typically the phone bank ones. If this was a Microsoft question I'm shocked because they got it wrong. The reason why SOME manhole covers are round is because it makes it easy to roll manuver the manhole around not because a bigger circle can't fit inside a smaller one because a bigger square can't fit into a smaller one either. It's not because of the pressure, because the material is easily strong enough to handle the forces its subjected to. Not all "manhole" covers are round, phone banks/communications/drainage grates are often times square. It had to do with a standard established back in the day when men had to move them by hand. It just was plain easier to roll it into place and tip it over.