pi pie

IMG_2661With so few math holidays, we in the world of math take our pi/pie very seriously! So of course, on 3/14 we ate the delicious pies that our students brought in to share. Parents are always wonderfully generous about baking or buying pies. Monday, Pi Day, began a week of learning about circles (diameter, radius, circumference, center, chord), before we tackled trying to understand the ratio of the circumference of a circle to its diameter, which is what the 16th greek letter pi represents. While we ate, we listened to Sir Cumference and the Dragon of Pi. This book is one in a series of math stories. The books use math vocabulary in silly, subtle and not-so-subtle ways to make the words more memorable (Sir Cumference, Lady Di of Ameter and their son Radius are the main characters. Per of Imeter, Countess Areana and twins Geo and Sym of Metry are also in some of the stories). 4th and 5th graders are being challenged to memorize as many digits of pi as they can, from the first 11 digits all the way up to 101 digits. An additional challenge is to memorize the digits in a second language. A classroom reward system is in place to encourage them to try and to reward their hard work.

Following Pi Day, we began working with circles by finding a circle’s diameter, radius, circumference and center. We discussed the relationship between a circle’s radius and its diameter (diameter = radius x 2 or radius = 1/2 diameter). Students were then challenged to answer this question: if you know your circle’s diameter, how can it help you find the circumference? We thought back to the story and many students were able to make the connection that it takes a little more than 3 diameters to make the circumference, 3.14 diameters to be more precise. We tested this on our circles and it works! Our circle’s diameter was 6.5 inches. We multiplied 6.5 x pi (3.14) to get 20.41 inches for the circumference. It turned out to be very useful to know the diameter, so that we didn’t actually have to measure the circumference (curved edges are mighty difficult to measure). We spent a day measuring a variety of round objects (diameters and circumferences). We used inches as our unit and reviewed reading the marks on rulers; we measured to the closest 1/4 of an inch (a few ambitious students wanted to measure to the closest 32nd of an inch). We then tested the accuracy of our measurements. Using calculators, did our diameters x 3.14 equal the circumferences? This step involved renaming our fractions (3 and 1/2 inches) as decimals (3.5 inches). Students love testing their answers and are thrilled when their results are accurate.

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Our final day of circles was learning how to use compasses (which is harder than it looks). Students enjoy using new tools and having time to practice and experiment. All in all, our week of circles was a rich learning experience.