Galton Board

Drop a ball and watch where it lands. At first glance it looks like pure chance: on its way down the ball bounces off a row of pins, going left or right with equal probability. But release dozens or hundreds of balls and something surprising happens — the bins below always form a characteristic bell shape. Most balls end up near the centre, because there are many possible routes to get there. Only a few reach the outermost bins, because that requires a long run of bounces to the same side, which is unlikely.

Mathematicians call the resulting distribution normal, because it describes a vast range of phenomena around us: people’s height and weight, measurement errors, noise in electronics, test results, the spread of biological traits or the motion of gas molecules.

This simple yet striking experiment was described in 1889 by the English scientist Francis Galton. The board he designed is not only a playful attraction but also a vivid demonstration that even apparent chaos can conceal an order of its own.