Where Does π Come From? — The Rolling-a-Circle Proof

Added: 2026-05-16

[00:00:02]You've seen this symbol all your life.

[00:00:04]But have you ever asked what it actually means? It's just a ratio built into every circle. Let me show you. Grab any circle. Doesn't matter how big or small.

[00:00:15]There are two dist. Straight across.

[00:00:18]That's the diameter. And once around the edge, that's the circumference.

[00:00:24]Now roll that circle along a flat line.

[00:00:26]One full turn. Watch how far it travels.

[00:00:31]That distance is exactly the circumference.

[00:00:35]Here it is the rolled distance. That's C. And here's the diameter underneath.

[00:00:40]That's D. Divide C by D. What do you get? 3.14 every single time.

[00:00:46]Try a coin. Try a planet. Try a pizza.

[00:00:49]The ratio doesn't care how big the circle is. It's always the same. It's built into geometry itself.

[00:00:55]We give that constant a name. Pi.

[00:00:59]And that's why every circle's circumference equals pi * it comes from where does pi r come from the area of a circle. We made that one too.

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