Pi Day: How to calculate pi using a cardboard tube and a load of balls

Balls in a box

Grab a few balls and get calculating pi

Aleksandr Elesin/Alamy

Pi Day, which occurs every 14 March – or 3.14, in the US date format – celebrates the world’s favourite mathematical constant. This year, why not try an experiment to calculate its value? All you’ll need is a cardboard tube and a series of balls, each 100 times lighter than the next. You have those lying around the house, right?

This experiment was first formulated by mathematician Gregory Galperin in 2001. It works because of a mathematical trick involving the masses of a pair of balls and the law …

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