WHAT IS PI?

Pi is the relationship between the diameter of a circle and its circumference.

DIAMETER is the distance straight across the middle of a circle. CIRCUMFERENCE is the distance around the outside of the circle.

The circumference of a circle is about three times longer than its diameter.

D + D + D = C or D x 3 = C

Pi is about 3. More precisely, the number for pi is closer to 3.14159265359. (But even that’s not exactly right — keep reading below!)

In math, the symbol for pi looks like this:

TEST IT OUT!

Not sure pi is real? Find out for yourself with some science!

Gather the following materials:

Tape measure
Ruler
Cylinders of various sizes (like soup cans, paper towel rolls, drinking cups…)
Paper and pencil or pen
Calculator

Then just follow these directions:

First, remember that circumference is the distance around the cylinder or circle, and that diameter is the distance across a circle.
With the tape measure, measure the circumference of one cylinder and write down that value.
With the ruler, measure the diameter of the cylinder and write that down next to the circumference.
Repeat steps 2 & 3 for all of the cylinders you’ve collected. Write down the values for each cylinder on a new row.
Look for a relationship between each cylinder’s circumference and diameter. How many diameters would you need to equal one circumference? That’s pi!
To get a more precise answer, use the calculator to take the circumference and divide it by the diameter. How close is your answer to 3.14? Think about why your answers are probably NOT going to be exactly right because your measurements won’t be perfect… and 3.14 is just an approximation of pi anyway!

SUPER LONG

Here’s just the first 100 decimal places of pi:

3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679 …

The three dots means that the number goes on and never ends! In 2021 researchers in Switzerland used a supercomputer to determine the value of pi to 62.8 TRILLION decimal places. That’s a lot!

PI CRAFT

Combine your math skills with your artistic skills!

If you’ve got lots of colorful beads (for bead bracelets) or different colors of craft paper (for paper chain garlands), you can make “pi art” that only kids as cool as you will understand! Whether you do this with beads or paper, the important thing is that they’ll need to be in 10 different colors.

For these instructions we’ll use the example of making bead bracelets, but the same concept works for paper chains.

What you’ll need:

Beads in 10 different colors
Cord for bracelets
Scissors to cut cord
Paper and pencil or pen

Write down on a piece of paper the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. Next to each number write the name of one of the color beads you have. Each color should only be assigned to ONE number (for example, if you write “0 = red” then no other number can be red). Using that as your guide, start placing beads on your bracelet cord in “pi order” for as many decimal places as you want. When you’re done placing beads, cut the cord leaving enough space at each end so you can tie the ends together.

The first 100 decimals places are listed above — with the beads and cord you have, how many digits can you make?

SPECIAL NOTE

Thanks for the books!

During each day of “Pi Week” we are sharing readings from the first five “Sir Cumference” series of math adventure books on social media. We want to give a special shout-out to the creators of those books — writer Cindy Neuschwander and illustrator Wayne Geehan — for the incredible job they’ve done. You can learn more about these books at the Penguin Random House website.