Discovering Pi

This book is all about finding measurements of circles and the parts of circles that were defined earlier in this unit.  When working with measurement and circles, the greek number pi is used frequently.  Circumference of a circle is the distance around the circle.  Please do the following activity to understand why circumference is associated with pi.

The following activity will help you understand why pi is associated with circles.  You will need string, a ruler, 3 or 4 different sizes of circles and paper.


1. Work in groups of 3 or 4.

2. As a group, use your string to "wrap" the distance around one of the circles marking or cutting the string where it meets the beginning.

3. Unwrap the string and use a ruler to measure its length to the nearest millimeter.

4. Use your ruler to measure the diameter of that circle to the nearest millimeter.

5. Record your results in a table similar to the one below:

Table for Pi 

6. Repeat this process two or three more times with the other sizes of circles, recording the measurements in the table as you go.

7. Use the data gathered to find the ratio of the circumference to the diameter and fill in the third column of the table.

*Note: If you are working alone, you need to do this for at least 3 circles.

Discussion: What do you notice about the number you find for the ratio of the circumference of a circle to the length of its diameter?



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