Recently I celebrated with a pizza pie – that’s American for pizza – to mark Pi Day, the day all Americans celebrate pi.
As every school-kid knows, unless they were away that day, pi (or π) is the constant relationship between a circle’s circumference and it’s radius. It is 3.14159… (with an endless string of numbers after that).
Thankfully Americans write dates the wrong way around, which is why Pi Day is on 3/14 (the third month and the 14th day). If it was an Aussie tradition, Pi Day would be on the 3rd day of the 14th month.
After mathematicians worked out pi about 4000 years ago they spent the next 3500 years refining its accuracy using clunky calculations.
Then the genius Issac Newton dreamed up a quicker method in about 1665 while he was in Bubonic Plague lockdown.
Despite all this effort, we still don’t know the exact circumference of a circle. We can be as accurate as we want, at least to the 11 trillionth decimal place (the current record), but never exact.
It’s a bit academic though. In the real world pi rarely needs more than a few decimal places. Any more than that is just nerds flexing their mental muscles.
Ironically it was in the home of Pi Day, the US, where one of the legislatures very nearly passed a Bill written by an amateur mathematician to set pi at exactly 3.2.
Everywhere else in the physical universe pi would be 3.14159… except in Indiana, where it would be 3.2.
Thankfully a university professor happened to be in the House as debate ended. He was invited to meet the “genius” who wrote the Bill but the professor declined, saying “I have already met as many crazy people as I care to”, which seeded some doubt among the Honorable Members.
Pi Day involves competitive recitations of pi to extreme decimal places (yawn!) and eating pizza pie (yay!). But calculating volumes using pi is also a thing.
Imagine a disc with radius (z) and thickness (a). The area of the disc is pi times the radius squared (pi.z.z), so the volume of the disc is the area times the thickness (a). Which gives a tasty formula = pi.z.z.a.