Pi Day

Pi-Day–Rose-Focht–HSLDA Blog

Pi, as most of us vaguely know, is a number that math people inexcusably named after a letter of the Greek alphabet. There’s a very simple equation that generates pi, which we have trouble remembering, and it has something do with circles. And no matter how big the circle is, it always has a pi. Pie, on the other hand, is best understood as apple, pumpkin, or lemon meringue, and almost always comes in circles too.

Today is March 14, or 3/14. The number pi comes out to 3.14-on-and-on-and-on, so mathematicians found the date pun unavoidable and hilarious.

I was mildly interested in Pi Day, being a homeschool mom and all, and also because we’re studying Ancient Greece at the moment. I had hoped that pi was discovered by Pythagoras (PY-thagoras?), because that would have made sense of why he named it Pi, but sadly, no. He is instead probably responsible for the Pythagorean Theorem, which is the length of sides on right triangles. (A squared plus B squared equals a C squared, which is memorable and can be sung like a Feist song.) I still have no idea why it’s pi and not, say, upsilon.


Pi, for the record, is the relationship between the CIRCUMFERENCE, the “circ” around, and the DIAMETER, the “dia-“, or across.  Pi = C/d. Meg and I considered this equation for a while.

So at this point, I went educational on the girls.

We got out little bowls and plates and traced them onto paper. (Tracing is easier than using flimsy compasses.) They colored their circles different colors and then made a column of the colors on the side, so we could measure each one. We talked about different ways to measure circles: from the center to the edge is called the “radius” (“Oh! Like Radius in the Sir Cumference books,” said Meg); across is the diameter, like Lady Di of Ameter; and around the edge is the circumference. So far, so good.


Then we measured each circle’s circumference and diameter. This turned into practice writing numbers the right way around and a lesson on the fine art of measuring with fractions, because the tiresome circles didn’t come in whole inches. Then we had a lesson on converting fractions into decimals on the calculator, because calculators don’t speak fraction. Then we had a lesson on rounding to two decimal points. Then we had a lesson on using calculators, because apparently it’s not an inborn skill. Kate, by this time, was long gone playing ponies.

We had a lesson on plugging numbers into equations: what number did we measure for the orange circle’s CIRCUMFERENCE? Okay, write that here. What number did we measure for the orange circle’s DIAMETER? Remember, dia- means “across.” Write that here. So type them into the calculator… nope, that’s the “multiply” button, you want the “divide” button… write that down…

It was a process.


Much to everyone’s credit, once the numbers were in, all of our pi calculations were between 3.0 and 3.3. I talked about how pi is a constant, which means no matter what circle you look at, anywhere, ever, if you measure it exactly, the relationship between its circumference and its diameter will always come out to about 3.14. Smile and nod.

Upon which, Meg went and painted a picture of a sailboat and I drank a medicinal Dr. Pepper.

Happy Pi Day, everyone. Please celebrate by not calculating pi five times with your kindergartener.  I think there’s .57 of a lemon pie in the fridge waiting for me.

Carolyn signature Montez font


Photo Credit: Second, third, and fourth images by Carolyn Bales.

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2 Comments on “Pi Day”

  1. Karen
    March 17, 2016 at 7:08 pm #

    Love it! My alma mater (MIT) always releases admissions decisions on Pi Day. Sometimes even on 3/14 1:59 PM EDT. I ran out of time to make a pie for my 5 year-old this year but it’s on the calendar for next year already!



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