There's more to those colliding blocks that compute pi

2025-03-13

[public] 516K views, 81.3K likes, dislikes audio only

4K

Two colliding blocks compute pi. Here we dig into the physics to explain why.

Next video on Grover's Algorithm: /youtube/video/RQWpF2Gb-gU

Instead of sponsored ad reads, these lessons are funded directly by viewers: https://3b1b.co/support

An equally valuable form of support is to simply share the videos.

Next video on Grover's Algorithm:

/youtube/video/RQWpF2Gb-gU

The original paper by Gregory Galperin:

https://www.maths.tcd.ie/~lebed/Galperin.%20Playing%20pool%20with%20pi.pdf

Adam Brown's paper on the analogy with Grover's Algorithm:

https://arxiv.org/pdf/1912.02207

Here's a lovely interactive built by GitHub user prajwalsouza after watching this video: https://prajwalsouza.github.io/Experiments/Colliding-Blocks.html

Matt Parker's Pi Day video:

/youtube/video/vlUTlbZT4ig

NY Times blog post about this problem:

https://wordplay.blogs.nytimes.com/2014/03/10/pi/

Timestamps:

0:00 - Intro

0:48 - Recap, the surprise pi

3:58 - The game plan

5:31 - How to analyze the blocks

14:59 - The geometry puzzle

20:05 - Small angle approximations

25:00 - The value of pure puzzles

SEV#7: https://youtu.be/RTCQYcOpmN4

The original version of this explanation (now unlisted): /youtube/video/jsYwFizhncE

------------------

These animations are largely made using a custom Python library, manim. See the FAQ comments here:

https://3b1b.co/faq#manim

https://github.com/3b1b/manim

https://github.com/ManimCommunity/manim/

All code for specific videos is visible here:

https://github.com/3b1b/videos/

The music is by Vincent Rubinetti.

https://www.vincentrubinetti.com

https://vincerubinetti.bandcamp.com/album/the-music-of-3blue1brown

https://open.spotify.com/album/1dVyjwS8FBqXhRunaG5W5u

------------------

3blue1brown is a channel about animating math, in all senses of the word animate. If you're reading the bottom of a video description, I'm guessing you're more interested than the average viewer in lessons here. It would mean a lot to me if you chose to stay up to date on new ones, either by subscribing here on YouTube or otherwise following on whichever platform below you check most regularly.

Mailing list: https://3blue1brown.substack.com

Twitter: https://twitter.com/3blue1brown

Instagram: https://www.instagram.com/3blue1brown

Reddit: https://www.reddit.com/r/3blue1brown

Facebook: https://www.facebook.com/3blue1brown

Patreon: https://patreon.com/3blue1brown

Website: https://www.3blue1brown.com