Why are manhole covers round? - Marc Chamberland

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.

[MattsMotorz]

The reuleaux triangle is used in rotary engines, it spins in the same way as shown in the video. Very cool!

[BoogsterSU]

Petition to make Rulo Triangle manhole covers.

[sonicpsycho]

Also, because when you make a hole sharp corners are weak points, areas or extremely high stress concentrations. While a circular hole is still a stress concentration, it's the lowest of any geometric shape.

[xden]

why does this channel consistently teach me things that I didn't know that I wanted to learn. ITS SO GOOD

[tommythai]

2:25
Partially true. We can indeed make surfaces of constant widths in 3 dimensions but the reuleaux tetrahedron is not one of them. The reuleaux tetrahedron is slightly wider edge to edge than corner to face. Rounding off 3 edges or 3 corners of a reuleaux tetrahedron will however, give you a surface of constant width - this specific occurrence is known as a meissner tetrahedron.

[JaySee]

A Reuleaux triangle also is the heart of a rotary engine.

[Owiko]

All this to find out that square manholes covers would fall in...

[shivaanumahendrarajan]

So pretty much, the answer is:
So the manhole cover doesn't fall in

[Sehemo]

Very good example of such an interesting topic. I really hope TED continues to do all sorts of educational videos.

[DmitryKiktenko]

What an awesome cartoon story was made for this lesson! I love cartoonist's humour in this one so much! Wise and intelligent caveman teaches geometry, riding a board, and that funny fall down into square hole. Great job!

[chromosoze]

Short answer: So the cover wouldn't fall in

Long answer: Because if you rotate a circle the distance between the bottom edge and the top edge will stay the same distance apart and they could act like a wheel.

[HansenSWE]

I paused an episode of my favorite show to watch this, because... manhole covers! Why _are_ they round?

[TheDrBB]

Is it just me or did 2:56 look extremely violent?

[youngshinyun]

Eureka...I have already known that other shape of manhole cover, such as triangle, square, and etc, could fall in, but the concept of curve of constant width.... is something new to me... Thank Ted-Ed...you are my great teacher...

[ЕвгенийВасин-эб]

Спасибо. Как всё просто, когда объясняют кратко и только суть. Удачи вам.

[deadasfak]

I was putting this episode off until I had nothing interesting to watch. This video was far more informative than the title suggested. It's like anti clickbait. Thanks for the surprise.

[antiawarenessawarenessclub]

The video explained in depth WHY a shape like a circle wouldn’t fall on, then showed you the practical application

And they say maths is useless

[shimi_ek]

Someone said that it would be easier to just say "so they can't fall through the hole."
- showing us exactly how the science IS taught at schools instead of how it SHOULD be taught.

[friebender]

I love those kind of topics. Thanks Ted-Ed :)

[Gaudentic]

I dont allways comment on a youtube video, but when I do, I do it because I am quite impressed.
cheers-.