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*Contributor: Erika Wargo. Lesson ID: 12576*

What do pi and pie have in common, besides two letters? Pi helps you calculate the circumference of a circle, and helps bakers make pies! Learn the parts of a circle and how to use them to measure!

categories

subject

Math

learning style

Kinesthetic, Visual

personality style

Beaver

Grade Level

Middle School (6-8)

Lesson Type

Quick Query

Let's say you are a swimmer practicing for the Olympics. You need to swim a certain distance, so you lap around the edge of your round swimming pool.

- How do you calculate the distance around the swimming pool?
- What information would you need to know?

Many objects that you use and see every day are circles.

A circle is made up of points that are the same distance from the center. There are three main parts to a circle.

- Do you know the names of the three parts labeled on the circle below:

Check and see how you did.

Click on each + sign to read a description of each part of the circle:

Now that you are familiar with the parts of a circle, learn more about calculating the circumference of a circle with an activity.

Complete the following steps:

- Go to Circumference (Scholastic StudyJams!) and click on the Step-by-Step button to watch how to calculate the circumference of a circle.

- Click on the NEXT and SHOW ME buttons to progress through the steps.

- Click on WATCH OUT! to review facts about pi.

Next, watch this video from Don't Memorise to understand where pi came from and why we use it.

*What is the Circumference of a Circle? | Perimeter of a Circle | Don't Memorise*:

After you have completed the activities above, consider the following:

- What is circumference?
- What is the formula for finding circumference?
- What value of pi should be used in the formula?
- If you know the radius of a circle, how do you calculate the diameter?

At the beginning of the lesson, you were presented with a question about a circular pool:

- How do you calculate the distance around the swimming pool?
- What information would you need to know?

- What information do you think is needed in order to solve the distance around the pool?

Review the example below:

- If the radius of a circular pool is 5 feet, what is the circumference of the pool?

To find the circumference of a circle, use the formula, C = pi (Π) x D.

You are given a radius of 5 feet, so to find the diameter, multiply the radius by 2. 5 x 2 = 10, so the diameter is 10.

Since the diameter is 10 and pi is 3.14, 10 x 3.14 = 31.4 feet. The circumference, or distance around the circular pool, is 31.4 feet.

One way to remember the formula for circumference is to think about a cherry pie:

"Cherry pie is delicious" or C = Π x D.

In the formula, think of the "C" for circumference as "cherry," the Π symbol as "pie," and the "D" for diameter as "delicious."

In your math journal, write a response to the following:

- Draw and label the parts of a circle: diameter, radius, circumference.
- What information is needed to calculate the circumference of a circle?
- Explain a time you would need to find the circumference of a circle, other than the example given in this lesson about the pool.

In the *Got It?* section, you will practice calculating the circumference of a circle as you complete interactive practice and move around a life-size circle.