Circles in Geometry

Overview: Grade school geometry doesn't have to get into a detailed lesson on Pi to communicate the basics of this constant.
Teacher Preparation: flexible tape measure.
Procedure Ideas:

• Break into groups, giving each group something circular to measure, both the diameter and the circumference. Then divide the circumference by the diameter to get a number. When all groups are finished, have each group read off the answer to the division problem. Use this as a lead-in to your further discussion of circle properties.
• Ideas of circular items to measure: basketballs, softballs, globes, hoola-hoops.
• A whole-class activity could be: have one student stand in the middle of the gymnasium, holding one end of a known length of string. Then walk the other end of the string around to form a circle, placing students evenly on the imaginary circumference. When finished, you should have your students representing a fairly good circle, with one in the middle. Use the tape measure to find the diameter, using the center student for accuracy in measuring through the circle's center. Then measure the circumference as well. Calculate for Pi.
• Discuss real-world applications for knowing Pi to estimate circumferences of objects or areas: How long a piece of paper must be to cover a round container for an art project; finding the actual diameter of the earth by using a globe with a distance scale to first determine the circumference.
• For everything you wanted to know (or didn't want to know) about Pi, there is a Yahoo site.
• Assign students to work with their parents in finding uses for estimating circle circumferences at home. Starting points might be length of a circular sidewalk around a flower bed, how much paint needed to cover a round structure, how long a piece of wire is needed to make a round perch for a bird feeder.

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