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Learning Objectives 1.You will construct a circle using a compass. 2.You will draw the following parts of a circle: center, radius, diameter, and chord. 3.You will construct a circle without using a compass.

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Developed by Ivan Seneviratne

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What is a Compass? A compass is a hinged device for drawing circles.

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Galileo's Proportional Compass The first proportional compass was invented in Padua in 1597. The inventor, Galileo, saw three main uses of his compass: 1.As a bomber's sight, 2.Calculation of the height of a star above the horizon and 3.Measuring the inclination of the slopes of a wall.

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needle lead Preparing the Compass 1.Sharpen the lead. 2.Adjust the needle and the lead so that the tip of the needle extends slightly more than the lead.

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Using the Compass 3.To draw a circle, apply enough pressure to the needle by holding the compass handle between thumb and index fingers. 4.To complete drawing the circle, revolve the handle clockwise.

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Drawing without Compass Here's a way to draw a circle using something normally already on hand.... 1. 1. Simply cut a strip of 1" wide and a little longer than the radius of the circle needed. 2. Punch a hole in one end, where the point of a pencil could be placed through for drawing. 3. Place a pin on the other end precisely the distance from the pencil hole which represents the radius of the circle.

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Drawing without Compass To draw a circle, stick the pin into your drawing surface, put a pencil in the hole and rotate around the pin 360 degrees.

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World Freehand Circle Drawing Championship 2007 Alexander Overwijk, a teacher from Ottawa, Canada, is one of the fastest Circle Drawers in the world. He draws a close-to-perfect 3 foot wide circle in less than two seconds.

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Your Turn 1.Draw a circle that has a radius of 4 cm on the given origami paper. 2.Cut the circle into a semi circle and a quarter circle. 3.Paste the quarter circle and the semi circle on a Journal Writing sheet. 4.Find the perimeter of each shape. 5.Show clearly how you derived the answers.

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Images - http://apod.nasa.govhttp://apod.nasa.gov http://www.britannica.com This presentation is developed by Ivan Seneviratne © 2007 purely for personal use. ivanthexplorer@yahoo.co.uk Acknowledgments

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