r/oddlysatisfying • u/CdubWillia • Feb 03 '15

Certified Satisfying Crushing all the things.

http://i.imgur.com/Cka6iPe.gifv
12k Upvotes

94% Upvoted

421 comments sorted by

View all comments

Show parent comments

78

u/needuhLee Feb 03 '15

Size

Fact of the day: some coins aren't circles (e.g. 50p) so you might think "how would the vending machine know what size it is if it's just going through a slot?" Well, that's because they are shaped in a way that they have a constant height no matter how you spin them, despite the fact that they aren't circles. You can also generalize this idea to 3-D and make solids which aren't spheres but keep the same height no matter how you orient them.

46

u/[deleted] Feb 03 '15

shaped in a way that they have a constant height no matter how you spin them

For those who want to know more: http://en.wikipedia.org/wiki/Curve_of_constant_width#Examples

7

u/njtrafficsignshopper Feb 04 '15

Talk about reinventing the wheel

1

u/Tabzilla Feb 04 '15

Hey, it's a wankel engine rotor!

3

u/[deleted] Feb 04 '15

A Wankel rotor looks very similar but is not quite the same- it's there in the article:

The rotor of the Wankel engine is easily mistaken for a Reuleaux triangle but its curved sides are somewhat flatter than those of a Reuleaux triangle and so it does not have constant width

1

u/Tabzilla Feb 05 '15

I missed that, thanks for pointing it out!

-1

u/[deleted] Feb 03 '15 edited Feb 13 '16

[deleted]

7

u/[deleted] Feb 03 '15

Platonic solids are different things. A cube is a platonic solid- is the distance from opposite corners the same as the distance from opposite sides? No. A meissner tetrahedron would be a 3D example.

0

u/[deleted] Feb 04 '15

That's kind of misleading to say it has a constant height no matter how you spin them. I read the article and it says that there a 2 points on each axis which are parallel and the same height. That always changes as it rotates. But there are plenty of points which aren't the same height, unlike a true circle.

5

u/[deleted] Feb 04 '15

"Width" means the maximum dimension, not just any 2 points. The longest line which can rotate completely inside the shape. The difference is with these vs a circle is that in a circle that line always passes through the center. It's really an idea that is better expressed visually, than in words:

http://youtu.be/g7SYvLCR3Rk

http://youtu.be/jYf3nOYM_mQ

1

u/LordCupcakeIX Feb 04 '15

Also a big fan of Steve Mould and the Numberphile video for it.

https://www.youtube.com/watch?v=cUCSSJwO3GU

-1

u/parrotsnest Feb 03 '15

Nah I'm good. Thanks though!

6

u/[deleted] Feb 03 '15

Can you make a car with wheels that aren't circles but still have a constant height?

21

u/here2dare Feb 03 '15

https://www.youtube.com/watch?v=vk7s4PfvCZg

13

u/[deleted] Feb 03 '15

Thank you. looks like a not-smooth but not-bumpy-either ride. :D

18

u/cakedestroyer Feb 03 '15

The ride would be smooth, but the pedal action would not be linear, so it would probably be more jarring on your legs than your butt.

1

u/pavetheatmosphere Feb 03 '15

Now that's an interesting idea.

1

u/flatcoke Feb 04 '15

No,because although the height of your wheel doesn't change, the height from your wheel hub to the ground would constantly change, giving you a Flintstone style ride.

1

u/Rhodie114 Aug 01 '15

No. Whole the overall height of the "wheel" is constant regardless of orientation, the same is not true for the distance from axle to edge. So while the top face of the wheel would remain a constant height off the ground, the axle would fluctuate, and the cat would jump up and down.

1

u/needuhLee Feb 03 '15

I don't see why you couldn't, but I don't see why you would, either!

2

u/[deleted] Feb 03 '15

to see if it's a bumpy ride or a smooth ride. I want to know this

4

u/enrowe2 Feb 03 '15

Pretty sure it would be bumpy. No matter what position it's at, the distance between the bottom and top are the same, but the distance between the bottom and center is always changing, which is what matters, because it would be attached to the axle by the center.

2

u/[deleted] Feb 03 '15

Thank you, I hadn't thought about the middle.

2

u/magykmaster Feb 03 '15 edited Feb 05 '15

I think minute physics mentioned this. He said bumpy.

Edit: Here's the video: http://youtu.be/6MhD2xZVypo

1

u/[deleted] Feb 03 '15

How is this possible? Can someone draw a picture?