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# What Is Pi?

Learn what the number pi means using a simple arts-and-crafts project. Then find out why you’ll want to celebrate this newfound knowledge on March 14.

By
Jason Marshall, PhD
Episode #97

What is pi? If you’re so inspired, feel free to insert your own favorite punchline about delicious baked goods here. Although I’ll spare you the humor since we are, of course, not talking about that kind of pi (as in p-i-e). Instead, we’re talking about π (as in the sixteenth letter of the Greek alphabet). And our timing couldn’t be better since we’re fast approaching a pretty big holiday in the hearts of true math fans—pi day on March 14. Why all the fuss over a number? And why March 14? Stay tuned for the answers.

## What Is the Meaning of Pi?

As you may have learned in school (but perhaps never fully appreciated), the origin of the number that we call “pi” for short (and usually write with the Greek letter π) that’s equal to approximately 3.14 has a very easy-to-understand meaning. To see what this meaning is, we’re going to do a little arts-and-crafts project that you can complete using nothing more than a piece of paper, a pencil, some string, and a pair of scissors. Or, if you prefer, you can actually do the whole thing in your head.

## How to Draw a Perfect Circle

The first thing you need to do is use some string to help you draw a perfect circle on your piece of paper. Of course, no matter how hard you try your circle won’t be “perfect,” but if you’re careful you can do a pretty good job. To draw your circle, start by cutting about a 3-inch piece of string (or bigger if you’re working with a piece of paper that’s larger than a normal sheet of binder paper). As you’ll see, this string is going to represent the diameter of your circle. Now, draw a dot near the center of your paper and pin the middle of the string down right on top of this dot with your finger (you can find the middle of the string by folding it in half). Then hold the loose end of the string up against the lead of your pencil, pull it away from your pinned down finger so that the string is taut, and trace out a circle by moving the pencil around in a…well…circle.