Why Manhole Covers are Round

Manhole covers are everywhere these days, and many people wonder why they are round instead of any other shape.

There are several reasons that a manhole cover is round.  The main reason is that if it is round, the cover can’t fall through the hole regardless of what direction it is put in.  If the manhole cover is a rectangular shape and the cover is turned so that one side is aligned to the diagonal of the hole in the ground, then the cover will fall into the sewer.  Another reason a manhole cover is round is that the tunnel leading down to the sewer is a round tube.  A round tube is the most material efficient and strongest way to protect itself against the compression of the dirt and soil around them.  Because the tube is round, then the cover has to be round too.  Also, manhole covers are round so that they are easier to machine.  Round objects can be made using a lathe, which assures precision manufacturing.  If a manhole cover is not precise, it is easily lifted up by passing cars.  Basically, round manhole covers can be made more perfect than any other shape, which prevents it from coming out of the ground easily.  A smaller, but still important reason that manhole covers are round is that they can be rotated in any direction, and it will still fit perfectly in the hole.  This saves a countless number of minutes for the workers that take care of the sewers.  Circular manhole covers are also easier to move around.  Because of the circular shape, a worker can simply roll the manhole cover to its rightful spot in the world.  An extremely minor reason is that humans are somewhat round, so it is a better fit.  Finally, it is easier to dig a circular hole.  Rectangles and triangles are difficult to dig because of the angles.  

            Manhole covers are circular for many reasons, so for the people that wonder, now they know why.




 P.S. I wrote this as an essay for math