Measuring Circles

Lesson Plan - Get It!

Audio:

In the previous Related Lesson, found on the right-hand side, you learned the four parts of a circle.

Draw a circle on a piece of paper. Then, draw and label the following parts. Make sure to use a ruler or straightedge to help you create straight lines.

• circumference
• diameter
• radius
• chord

In this lesson, you will learn how to measure circumference, diameter, radius, and chord.

Finding the diameter, radius, and chord is easy.

• How do you think you should measure each of these parts?

To find the diameter, radius, and chord, use a ruler to measure each part. Throughout this lesson, you will measure everything in centimeters.

Finding the circumference is a little more challenging. In most cases, you cannot straighten the circumference out, so you have a nice straight line to measure.

• How do you think you should measure to find the circumference?

To measure the circumference, you need a ruler and a piece of yarn. Lay the yarn over the top of the circle's outline, creating a circle with the yarn. You want to create a yarn circle the same size as the circle you are trying to measure.

Once you have created the yarn circle, cut the yarn so it is the exact circumference length. Then, pick the yarn up and straighten it into a straight line.

Now, it is easy to use your ruler to measure the circumference!

Now that you know how to find the circumference, diameter, radius, and chord, move to the Got It? section to practice measuring circles and seeing the relationships among the parts of a circle.