Lesson plan

Find the circumference of a circle by using a formula

teaches Common Core State Standards CCSS.Math.Content.7.G.B.4 http://corestandards.org/Math/Content/7/G/B/4
teaches Common Core State Standards CCSS.Math.Practice.MP7 http://corestandards.org/Math/Practice/MP7
teaches Common Core State Standards CCSS.Math.Practice.MP8 http://corestandards.org/Math/Practice/MP8

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Big ideas: Pi is the constant of proportionality for circles. The circumference of a circle can be found by using the formula c = 2πr. This lesson introduces how to find the circumference of a circle. The task involves students using a piece of string or pipe cleaner that is the length of a circle’s diameter. Students then measure how many times the diameter of a circle wraps around the circumference. Students will repeat this investigation four times and then analyze the data. From this exploration, students will find the diameter of any circle wraps around the circumference about three times. Finally, students will derive the formula to find the circumference of a circle, c = 2πr. Vocabulary: diameter, radius, perimeter, circumference, pi (π) Special Materials: Rulers Pipe-cleaners or string Scissors