Learning Objectives1. 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.

Developed byIvan Seneviratne

What is a Compass?

A compass is a hinged device for drawing circles.

Galileo's Proportional CompassThe 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 and3. Measuring the inclination of the slopes of

a wall.

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.

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.

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.

Drawing without CompassTo draw a circle, stick the pin into your drawing surface,

put a pencil in the hole and rotate around the pin 360 degrees.

World Freehand Circle Drawing Championship

2007Alexander 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.

Your Turn1. 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.

Images - http://apod.nasa.gov http://www.britannica.com

This presentation is developed by Ivan Seneviratne © 2007 purely for personal use.

ivanthexplorer@yahoo.co.uk

Acknowledgments