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        Properties of Circles

        Students practice circle geometry by learning to draw a perfect circle using a radius and finding the center of a circle by folding it into quarters.

        Lesson Summary


        The students are asked to consider how to draw a perfect circle, and learn to do so using a line segment called a radius. They also learn to fold a circle in two directions symmetrically to find its center. This activity is motivated by a CYBERCHASE episode in which the CyberSquad set out to rescue a magic ring from Hacker and deposit it in a safe place.

        Grade Level:


        Suggested Time

        60 minutes

        Media Resources

        Tricking Hacker QuickTime Video
        Finding the Circle's Center QuickTime Video


        String, spaghetti (uncooked)
        Pre-cut paper circles, rulers, blank paper
        Assessment: Level A
        Assessment: Level B
        Answer Key

        The Lesson

        Part I: Learning Activity

        1. Read the following: "Hacker has stolen the Totally Rad Ring from Radopolis, home of all the skating radsters. He can fill every one of his wishes, including attacking MotherBoard. The CyberSquad join up with Slider, a radster, to switch the real ring with a fake one."

        2. To make the fake ring, the Cyberchase kids and Slider must figure out how to draw a perfect circle. Ask students to try to: a) draw a perfect circle by hand, and b) figure out how they could use a piece of string or a piece of spaghetti to draw a more perfect circle.

        3. Tell the students that they will watch a video in which the CyberSquad tries to solve this problem and that they will hear a new word. Ask them to listen carefully for it and figure out what it means.

        4. Suggest that they could try to write something down to help them remember the new word [To the teacher only: the word is "radius."]

        5. Show the Tricking Hacker QuickTime Video .

        6. After watching the video segment, a) discuss the new word and its meaning: (a radius is the distance from the center of a circle to any point on the edge); b) what machine Slider used, and why it worked; and c) why they needed two radii to make a ring (because of the width of the ring itself).

        7. Distribute rulers and pre-cut paper circles (coffee filters are a good inexpensive choice).

        8. Ask students to a) approximate or estimate the location of the center; b) find the center; c) prove that the point they find as the center IS in fact the center of their paper circles, and d) measure the radius of the circle, based on their center.

        9. Tell the students they will watch another video segment, in which: "The Cyberchase kids, Slider and Digit switch the ring that Hacker has stolen with a fake one. To keep the real ring safe, they must put it in the exact center of the Circle of Supreme Safety, a place in the woods with a protective spell. Jackie and Inez must find the center quickly. Watch and see how they do it and compare their method to yours."

        10. Show the Finding the Circle's Center QuickTime Video .

        11. Lead a class discussion of the students' ways of finding the center, and comparing their methods to the method Jackie and Inez used in the video segment.

        12. Ask the students to identify circles around the classroom, and to see if they can find the centers and radii.

        Part II: Assessment

        Assessment: Level A (proficiency): Students are asked to measure the radii of several circles of different sizes, and of a ring. 

        Assessment: Level B (above proficiency): Students are asked to measure the radii of several circles which are even multiples of each other, and are introduced to and asked to deduce the size of a diameter.


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