This project, courtesy of Jayne Fountain-Miller, a science instructor at Ohio's East Canton Middle School, is a perfect example of hands-on learning: kids measure a variety of circles in the real world--tires, flower pots, hula hoops--and do calculations that show how pi never changes. No matter what size a circle is, it's always about three times longer around than it is across.

PROJECT:
To measure different circles and determine the value of pi (the Greek word for circumference)

GOAL:
To show that the value of pi constant and not dependent on size

AGES:
11 to 13

MATERIALS:
• Paper, pencil, and clipboard
• Calculator
• Measuring tape or string and yardstick

STEP 1
Each child should mark off four columns on a piece of paper. Label them "Object", "Circumference" (C), "Diameter" (d), and the last "C/d = ?".

STEP 2
Without explaining what you expect them to find, turn the kids loose outdoors or indoors to look for as many circles as they can. They should stick with circles they can wrap a measuring tape around--a picture of a circle won't work, for example, because the measurements will be too imprecise.

STEP 3
Instruct the kids to carefully measure the distance around the circle (the circumference) and the distance across the circle (the diameter). Make sure they write down each number and translate any fractions into decimals (23 1/4 = 23.25; 12 5/8 = 12.625, etc.). Tell them to divide the circumference by the diameter and record the result. Repeat the process for a number of different circles.

STEP 4 Have the kids compare their results and tell you what they found. Most of their answers should be around three and several should be close to 3.14, if not exactly that. Ask them if the size of the circle made any difference in the end result (how does the a CD compare to a bicycle tire?). You can point out that the distance around any circle is always just a little more than three times the distance across it.

Finally, get a little dramatic: Tell them that pi is a magic number, an endless number, one that no mathematician or computer has ever seen the end of. Tell them that even though everyone says pi equals 3.14, pi actually equals 3.1415926535897932384626433832795. . .