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Why are manhole covers round? – Marc Chamberland

View full lesson: http://ed.ted.com/lessons/why-are-man…

Why are most manhole covers round? Sure it makes them easy to roll, and slide into place in any alignment.

But there’s another, more compelling reason, involving a peculiar geometric property of circles and other shapes.

Marc Chamberland explains curves of constant width and Barbier’s theorem.

Lesson by Marc Chamberland.

Animation by Pew36 Animation Studios.