Why Are Manhole Covers Round?

School has been CRAZY lately and I have been frantically trying to keep up with the reading.  It shouldn’t be a problem except I still haven’t been able to kick this habit of sleeping.  Every day, I just can’t seem to help it.  Anyway…

I got Outliers: The Story of Success by Malcolm Gladwell for Christmas (thanks Jaime!) and I haven’t been able to get around to reading it but I picked it up yesterday for fun and started reading.  It is amazing!  Click here if you want to see Gladwell talking about it (WARNING! He is as ugly as the day is long!)

I love Gladwell’s books.  If you want a book that makes you think, try anything written by him. (The Tipping Point: How Small Things Can Make a Big Difference, Blink: The Power of Thinking Without Thinking)  I have copies of both of them all so if you’re around, ask and I’ll loan one to you.

Outliers asks the question: ‘Why do some people succeed more than others?’  It’s not why you think.  Everyone would like it to be because you’re smart or talented and it was just going to turn out that way, but instead, hard work, opportunity, and just dumb luck have a bigger part to play than you might like to admit.  Today I read a question that Microsoft used to ask in it’s entrance interviews.  Microsoft gets lots of freaky smart people applying for jobs but they don’t just want nerdy smart anymore (I imagine they’re all stocked up on that anyway). 

They want people who think differently than other people so they ask every applicant:

Why are manhole covers round?

There isn’t just one answer but if you can come up with one (or more than one) you are the kind of thinker they are looking for.  So let’s give it a try!  Comment below and leave an answer.  I’ll be back in a couple of days to give you a list of the answers they have heard over the years.


2 thoughts on “Why Are Manhole Covers Round?

  1. # A round manhole cover cannot fall through its circular opening, where as a square manhole cover may fall in if it were inserted diagonally in the hole.
    #Easier to manufacture.
    # 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.
    # 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 horizontal boring mills.
    # 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.
    # It’s easier to dig a circular hole.


  2. It is a mandated tradition from long sitting Mayors. They are real fat and round. Their competition is not as rotound as they have not had as many “fat cat” lunches. So, their competition can fall through the hole but the get stuck at the waist with their impressive girth–do I get the job at Microsoft?


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