Hidden in π

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Pi Day

One day a year when eating pie counts as homework.

Write the date the American way and 14 March becomes 3/14, the first three digits of π. Maths lovers have taken the hint: every year on 14 March there are pies, digit-reciting contests and a great many circles.

Pi Day is 14 March, every year.

Where it comes from

Physicist Larry Shaw held the first Pi Day at the Exploratorium, the San Francisco science museum, in 1988. In 2009 the US House of Representatives passed a resolution backing it, and in 2019 UNESCO named 14 March the International Day of Mathematics, first celebrated in 2020.

The date has a couple of extra coincidences: Albert Einstein was born on 14 March 1879, and Stephen Hawking died on 14 March 2018.

Other π-shaped days

  • 22 July: Pi Approximation Day, for the fraction 22/7 (written day first, 22/7).
  • 14 March at 1:59 pm: for the purists, 3.14159.
  • 14 February: not π at all, but a good day to find out how far apart two names are in π.

Pi Day in the classroom

Everything here works for a class of mixed ages, needs no sign-up and keeps nobody's details. Pupils never have to type their own phone number: a birthday, a favourite number or a name works just as well.

  • Measure a circle: wrap string round plates, tins and bike wheels, then divide each circumference by its diameter. Collect the class's answers on the board and watch them crowd around 3.14.
  • Find your birthday: everyone looks up their birthday on the home page and the class plots roughly how deep each one hides (rounded is plenty). Who is deepest? Why do 8-digit dates hide deeper than 6-digit ones?
  • Memory relay: teams learn ten new decimals a day with the Memory Trainer, then recite them in turn on 14 March.
  • Name fight: two pupils put their names on the keypad and see which turns up first. Then ask: is that luck, or does a shorter name always win?
  • Dial a digit: pick a position, guess the digit, then dial it. One in ten guesses should be right. Count how many your class gets.
  • Talk about proof: is every number really in π? is a good way into the difference between "we checked" and "we proved".

Sources

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