# Welcome to math, where everything is cool if you know how it works

October 18, 2018 3:40 PM Subscribe

Geometry is neat:

Surface Area of a Sphere

Cake by Dinara Kasko

Morphing Cube

Slowly Filling a Maze

Pop-up cards

Milling Machine At Work

Church in Mogno, Switzerland

Two inverted magnetic bowls causing un-magnetized steel balls to organize into geometric patterns

Mandala Creator

Solar Photovoltaic Farm in France

Balanced coins

Hilbert curve

Rainy day in Tokyo

Let's trips

Cross Bridge Waltz

By Étienne Jacob

Hundreds more, mostly gifs, at the r/GeometryIsNeat subreddit

Surface Area of a Sphere

Cake by Dinara Kasko

Morphing Cube

Slowly Filling a Maze

Pop-up cards

Milling Machine At Work

Church in Mogno, Switzerland

Two inverted magnetic bowls causing un-magnetized steel balls to organize into geometric patterns

Mandala Creator

Solar Photovoltaic Farm in France

Balanced coins

Hilbert curve

Rainy day in Tokyo

Let's trips

Cross Bridge Waltz

By Étienne Jacob

Hundreds more, mostly gifs, at the r/GeometryIsNeat subreddit

OMG YES, showing this to my math fearing father. See, Dad? See why I like this???

posted by Abehammerb Lincoln at 3:56 PM on October 18, 2018 [1 favorite]

posted by Abehammerb Lincoln at 3:56 PM on October 18, 2018 [1 favorite]

Did...did you just turn the surface area of a sphere into the area under the curve of a sine-wave?

WITCHCRAFT, BLACK MAGIC I SAY!

posted by The Legit Republic of Blanketsburg at 4:04 PM on October 18, 2018 [4 favorites]

WITCHCRAFT, BLACK MAGIC I SAY!

posted by The Legit Republic of Blanketsburg at 4:04 PM on October 18, 2018 [4 favorites]

Venus Flytrap Explains the Structure of an Atom

posted by The Underpants Monster at 4:17 PM on October 18, 2018 [3 favorites]

posted by The Underpants Monster at 4:17 PM on October 18, 2018 [3 favorites]

Thanks for these. I watched the milling several times. I've never really got math, but things like these make it real. The Sketchup sphere flattening one is so elegant.

posted by unearthed at 4:26 PM on October 18, 2018 [1 favorite]

posted by unearthed at 4:26 PM on October 18, 2018 [1 favorite]

Procedural symbols drawn by a mechanical plotter that uses a Lamy fountain pen (and Lamy blue ink). I've never heard of a plotter that uses an honest to god fountain pen.

posted by ardgedee at 4:33 PM on October 18, 2018 [3 favorites]

posted by ardgedee at 4:33 PM on October 18, 2018 [3 favorites]

I liked the Lemarchand Configuration solving itself.

“We have such... topologies... to show you.”

posted by GenjiandProust at 5:11 PM on October 18, 2018 [1 favorite]

“We have such... topologies... to show you.”

posted by GenjiandProust at 5:11 PM on October 18, 2018 [1 favorite]

This doesn't help me with my stupid Calculus homework today.

posted by rhizome at 7:38 PM on October 18, 2018 [3 favorites]

posted by rhizome at 7:38 PM on October 18, 2018 [3 favorites]

Oh, one of *those* people, huh?

When I was a kid, I liked to take a strip of paper (cut a half-inch off the edge of a sheet of paper), twist one end 180 degrees, and then tape the two ends together. Then I'd walk up to a victim and say "this only has one side". They'd say something like "no way" or "you're nuts". Then I'd give them a pencil and say "draw a line around the middle of one side."

For the big finish? Hand them a pair of scissors and say, "Okay, now cut it along your line."

posted by Twang at 7:46 PM on October 18, 2018 [2 favorites]

When I was a kid, I liked to take a strip of paper (cut a half-inch off the edge of a sheet of paper), twist one end 180 degrees, and then tape the two ends together. Then I'd walk up to a victim and say "this only has one side". They'd say something like "no way" or "you're nuts". Then I'd give them a pencil and say "draw a line around the middle of one side."

For the big finish? Hand them a pair of scissors and say, "Okay, now cut it along your line."

posted by Twang at 7:46 PM on October 18, 2018 [2 favorites]

my wife teaches math so some high-schoolers are definitely gonna see these.

posted by wellifyouinsist at 9:27 PM on October 18, 2018

posted by wellifyouinsist at 9:27 PM on October 18, 2018

OK, math people, what is wrong with this reasoning:

Let's find the surface area of a hemisphere. Taking infinitely many thin slices of the hemisphere, each of which has an area of 2*pi*r, the circumference, times dr, the height, it looks to me like the whole thing is an integral of 2*pi*r, which is, iirc, pi* r^2. Adding that to the other hemisphere, I get a surface area of 2* pi* r^2, which is half of what the correct formula really is. Please hope me!

posted by thelonius at 3:52 PM on October 19, 2018

Let's find the surface area of a hemisphere. Taking infinitely many thin slices of the hemisphere, each of which has an area of 2*pi*r, the circumference, times dr, the height, it looks to me like the whole thing is an integral of 2*pi*r, which is, iirc, pi* r^2. Adding that to the other hemisphere, I get a surface area of 2* pi* r^2, which is half of what the correct formula really is. Please hope me!

posted by thelonius at 3:52 PM on October 19, 2018

thelonius: here's an explanation of why that argument doesn't work. The short answer is that the slices don't have a height of dr—it's a more complicated expression than that.

posted by panic at 6:23 PM on October 20, 2018 [1 favorite]

posted by panic at 6:23 PM on October 20, 2018 [1 favorite]

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posted by Splunge at 3:48 PM on October 18, 2018 [1 favorite]