2. Parts of a circle The distance around circle O is called the circumference of the circle. It is similar to the perimeter of a polygon.

3. Parts of a circle In circle O, OB is a radius AC is a diameter

4. d Investigation For 3 different circular objects, measure the circumference and diameter. Divide the circumference by the diameter.

5. Take a class average of the numbers found when you divided the ratio C/d. What number did you come up with? Is it close to Pi? 3.1415...

6. The number  The ratio of the circumference of a circle to its diameter is the number . Circumference mCA =3.1416 mCA =5.8982 cm Circumference =18.5299 cm O A C