Circles - Diameter, Circumference, Radius and the Discovery of Pi

Kathleen Ryan Randolph Magnet School
7316 S. Hoyne
Chicago IL 60636
(773) 535-9015

Objective:

This seventh grade math lesson is designed to help students identify and
measure the diameter, circumference, and radius of a circle.
The students should discover the approximate value of pi through the
relationship between the diameter and circumference.

Materials Needed:

Various size circles, meter sticks, metric tape measures, rulers, scissors
Scotch tape, drywall tape, calculators, and table worksheet.

Strategy:

1. Identify the diameter, circumference, and radius of a circle.
2. Demonstrate for the students how to measure the diameter and circumference
on a circle. Explain that radius is half of the diameter.
3. Six various size circles are labeled A-F. Include many samples of the same
size circles.
4. Working in pairs or in groups have the students record the diameter and
radius of each circle using a ruler, tape measure, or meter stick using
centimeters. This information is recorded on a table worksheet.
5. The students then measure the circumference using drywall tape. The
drywall tape is placed around the perimeter of the circle and marked with a
pencil and then cut. The drywall tape is then measured on a ruler,
tape measure, or meter stick. The circumference is recorded on the table
worksheet.
6. After the students have recorded the information for circles A-F, ask the
students if they see a relationship between the diameter and circumference.
7. Divide the circumference by the diameter for each circle.
8. Discuss the results of circumference divided by diameter.
9. Compare the class' results with the standard value of pi(3.14159265...).
Write the symbol for pi (p) on the chalkboard.

Performance Assessment:

The students will measure the diameter of a record album or another circular
object (other than the previously used circles) and predict the circumference.
The students will then measure the circumference of another circular object and
predict the diameter.

Conclusion:

The students should have a clear understanding of the relationship between
circumference and diameter and be able to apply this knowledge to similar
situations.

NAME___________________________________________

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