Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

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/   
    
Associated Topics:
High School Conic Sections/Circles
High School Geometry
High School Triangles and Other Polygons
Middle School Conic Sections/Circles
Middle School Geometry
Middle School Triangles and Other Polygons

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/