Why are manhole covers round?  Marc Chamberland

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 Educator Marc Chamberland
 Director Adam Comiskey
 Artist Clarrisa Hanekon, Ryan Flynn, Calvin Bacon
 Script Editor Eleanor Nelsen
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The Reuleaux triangle is named after Franz Reuleaux, a 19^{th}century German engineer. This shape is the most easily constructed noncircular curve of constant width. There are many other curves of constant, some being infinitely smooth, while others having infinitely many corners. Visit the Museum of Math, Shapes that Roll and Mimematics, and watch the video on Reuleaux triangles. For more on manhole covers and their shape, visit Releaux Stones.
There are several coins around the world that are curves of constant width. This includes the American Susan B. Anthony silver dollar, the Canadian dollar coin (the “loonie”), and the British 50p coin. Such coins are as not as easy to counterfeit as circular coins yet their constant width makes them a logical choice for vending machines. Why?
You can find other interesting facts and figures about curves of constant width at this site. Interested in how you can drill a square hole? Watch this animation!
Learning more math concepts in a fun and unimaginable way interest you? Visit: Tipping Point Math by Marc Chamberland and learn about math as you have never imagined!
Marc Chamberland is the Myra Steele Professor of Mathematics and Natural Science at Grinnell College. He has published over 40 research articles in diverse areas such as number theory, combinatorics, differential equations, and dynamical systems. Marc is a huge proponent of experimental mathematics, a growing paradigm that uses computers to discover, conjecture and prove mathematical results. He has received support from the National Science Foundation to develop an advanced course in this area. Marc is passionate about communicating the beauty and excitement of mathematics. He has given about 100 talks and has reaches out to a general audience. His book "Single Digits: In Praise of Small Numbers" (Princeton University Press, 2015) describes magical properties of each of the numbers from one to nine. Marc is also the creator of the YouTube channel Tipping Point Math which shows "math as you never imagined."
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About TEDEd Originals
TEDEd Original lessons feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TEDEd original? Nominate yourself here »
Meet The Creators
 Educator Marc Chamberland
 Director Adam Comiskey
 Artist Clarrisa Hanekon, Ryan Flynn, Calvin Bacon
 Script Editor Eleanor Nelsen
 Narrator Addison Anderson