Maths

Why a dropped stick can find π: Buffon's needle

Dark wooden planks with amber and teal needles scattered across the seams, next to the title A dropped stick finds pi
30seconds
The 30-second version

Drop a stick on a floor of planks and count how often it lands across a seam. The count secretly contains π: for a needle as long as the plank width, the chance of crossing is 2/π, about 64%.

Throw thousands of needles, grab one yourself to see why the angle matters, and replay the famous 1901 experiment that got suspiciously close to the true value.

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