Activity
Buffon's needle
Drop needles on lined paper — and stumble onto π. The more you drop, the closer your estimate gets.
Tally
- Needles
- 0
- Crossing
- 0
When the needle length equals the line spacing, the probability of crossing a line is 2/π. Flip that around: π ≈ 2 × (total / crossings). Drop a few thousand and the estimate sharpens.
Drop a bunch of needles onto a sheet of paper ruled with parallel lines spaced exactly one needle-length apart. Count how many cross a line. Divide carefully — and out pops π.
How it works
If the needle length equals the line spacing, the probability of crossing a line is exactly 2/π. So if you drop N needles and C of them cross, π ≈ 2N / C. The more needles, the better the estimate.
This was first posed by Georges-Louis Leclerc, Comte de Buffon in 1733 — the earliest known geometric probability problem.