Why are Manhole Covers Round?
Date: 05/09/2000 at 15:16:45 From: Cira Parisi Subject: Geometry Why are most manhole covers round? Why aren't manhole covers on the streets squares (or rectangles)? I've tried searching on the Internet for the answer. I know that the shapes of many objects relate directly to their function.
Date: 05/09/2000 at 15:41:22 From: Doctor Douglas Subject: Re: Geometry Hi Cira, Thanks for sending your question to Ask Dr. Math. You are absolutely correct in saying that the shapes of many objects relate directly to their function. After all, it would not do to have wheels that were not round, right? (But see some of the Web sites below.) The standard answer to your question is that the circular shape possesses the nice property that it is impossible for the thin cover to drop through the hole (and possibly injure someone below). A square or rectangular cover could accidentally pass through the hole along the diagonal of the hole. For a site that address the manhole cover question directly, see "Manhole Covers" by Stephen E. Collins at: http://web66.umn.edu/Ramble/manhole/manhole.html And see "Rolling with Reuleaux," by Ivars Peterson: http://www.maa.org/mathland/mathland_10_21.html Hope that helps, - Doctor Douglas, The Math Forum http://mathforum.org/dr.math/
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