Saturday, November 5, 2011

How to draw a circle - by Nick

Note: last week, the topic at math circle was "geometry construction using ruler and compass". It took some practices for Nick to get used to using compass when he got home from the presentation. The next day he wrote this journal (edited version is posted).

Drawing a circle by hand is usually very hard. Sometimes the drawn circles look like blobs or ovals, but almost never good enough that you are satisfied with. That is why the compass was created. I am not talking about a compass like a device used to determine geographic direction, usually consisting of a magnetic needle or needles horizontally mounted or suspended and free to pivot until aligned with the earth's magnetic field that points north. I am talking about a V-shaped device for drawing circles or circular arcs and for taking measurements, consisting of a pair of rigid, end-hinged legs, one of which is equipped with a pen, pencil, or other writing utensil and the other with a sharp point providing a pivot about which the drawing leg is turned. It is sometimes also called pair of compasses.

To start, you should make the anchor pin come out of the frame the same length as the writing utensil. When draw a circle with a compass you must hold the compass by the top and apply some pressure on the sharp anchor point and twist the top handle of the compass using your thumb, index finger and middle finger, and then gently tilt the compass to turn, you will draw a very neat circle in a second.

Don’t apply too much pressure on the side with the writing utensil or the writing tips may break. When using compass, use one hand to twist the top handle of the compass, no need to twist your body or hand; use the other hand to keep the surface you are drawing on flat and fixed. Make sure not to hold the compass legs to draw otherwise you will change the radius of a circle and make it turn out weird.

Using this instrument you can draw light circles and then go over them in a darker shade. You can easily change the radius of the circles you draw from very small (when the two legs meet) to very large when you push them apart the farthest you can (but make sure you don’t break it). After some practice I can use a compass to draw perfect circles.

In math, you can use straight edge (ruler) and compass only to construct various geometries. Using the compass and ruler you can figure out exactly the midpoint of two points on your own, the tangent to a circle, and etc. A compass is a very useful tool for geometry although some people may not like it and use a computer program to generate circles and geometry, but where’s the fun in that? I really like using a compass and ruler to draw circles and lines and design patterns and I hope you will like it as well. Drawing a circle and making patterns is really fun. If you like math, you can go figure it out on your own or go to GeoGebra and download it on your computer and play around.

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