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Pi Day: Infinite ways to celebrate the magic of circles

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City Year celebrates Pi day

Throughout history, the humble circle has ignited debate, inflamed passions and intrigued many brilliant minds. Why is that? Just take a closer look at a circle near you, like the lid of your coffee cup or water bottle. Now, split that circle into two even halves by running a line through its center, and compare that length to how far your finger travels when its traces the perimeter of the lid once.

Wherever you buy your brew or your water, the distance around the circular lid will be a little over three times the distance across it! Try it again, with any circle—the wheel of a car, a ring or a clock on the wall—and the answer will be the same. The distance around is ALWAYS a bit more than three times the distance across the middle—in fact, about 3.14 times!

This is one of the mysteries of circles that you can help your students discover to celebrate Pi Day, an entire day celebrating the number 3.14, which of course takes place on 3/14 or March 14. While March 14 falls on a Sunday this year, any time is a good time to puzzle with your students over this number known as pi, or py, represented by the Greek letter π.

From the ancient Chinese to engineers at NASA, who used pi to figure out how to parachute equipment onto the planet Mars, including its successful touchdown last month of its Perseverance rover, many people have learned that pi comes in handy. In fact, pi is about as useful as it is long—that’s infinitely long. Want to test this out? You can see for yourself by exactly measuring the distance around the edge of a circle, or its circumference, and dividing by that distance across the middle, or diameter. You can divide those numbers all day, and you won’t finish! That’s why you’ll often see pi rounded to two decimal places—3.14.

To help you engage with students about pi and do some fun activities, check out the resources below. Feel free to adapt them to your current learning conditions—for example, distance learners can look for circles to measure at home and share their findings with the group online. Whether or not your students end up pursuing fields like science, technology, engineering or math, they’ll discover that pi is a very useful number to know!

Pi day math activities for students

  • Take the Pi in the Sky Challenge from NASA, which challenges students to solve math problems including measuring dust clouds on Mars or calculating the orbits of exoplanets. NASA also shows the many ways it uses pi for its projects, from designing parachutes to scouting for safe landing spots for its spacecraft, including its Mars rovers—Curiosity and Perseverance.
  • Check out these activities from the National Council of Teachers of Mathematics, which include throwing a digital pie at a cartoon octopus or measuring tree trunks to better understand the concepts of circumference and pi.
  • Using blocks of code to Bake a Perfect Pi(e)—students can share their projects and find new ones.
  • Pi poetry! Skip the Haiku, try a Pi-ku and other ways to write and rhyme about pi.  Distance learners can post their creations in a group chat or volunteer to read them aloud to their peers.
  • Adapt some of these Exploratorium activities to have fun with pi, which include learning about the strategy an 18th-century naturalist and gambler devised to estimate it!

In Greek, the word for circumference is perimetro (just like in Spanish)! The first letter in perimetro is p, which in the Greek alphabet is the symbol π.

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This story is an updated version of one published last March.

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