Ways to Remember the Meaning of Circumference, Radius, Diameter, and Chord
Date: 03/18/2004 at 16:20:34 From: Johnathan Subject: Circle parts If the minute hand touched the edge of the clock, would it be most like a diameter, radius, circumference, or chord of a circle? I have a hard time remembering what each of those means.
Date: 03/18/2004 at 16:45:45 From: Doctor Peterson Subject: Circle parts Hi, Johnathan. You need to learn these words! Since different people learn words in different ways, I'll show you a few ways to think about these circle terms. Some people just like pictures. Here is a picture showing what each term refers to: ooooooooo oooooo oooooo ooo / ooo oo / oo oo / oo o / o o radius/ o o / o o / o o / o o / o o---------------------*---------------------o o diameter o o o c o o e o o i o o o chord o c r oo-------------------------------oo oo oo n c ooo ooo oooooo oooooo e u ooooooooo m r f e Some people like definitions in words: The circumference is the outside of a circle, the distance around. A diameter is a segment through the center, from one side to the other. A radius is a segment from the center to the outside (circumference). A chord is any segment joining two points on the circumference. Some people like to make connections with other words or ideas. Here are some that may make the words memorable: "Circum-" means "around", as in Magellan's circumnavigation of the world (going around it); and it sounds like "circle", which is what the circumference really is! "Dia-" means "through"; and sometimes we say that two ideas are "diametrically opposed", meaning that they are on opposite sides, as far apart as possible. The diameter connects opposite sides of the circle. "Radius" reminds us of radiation; rays go out from the center of the sun, for instance, in all directions. Picture the circle as the earth's orbit, and a ray of light going from the sun at the center out to the earth. A "chord" is like a cord stretched across the circle. In fact, that's where the word comes from. The Greeks saw an arc (part of a circle) as a bow, and a chord as the bowstring. The word "arc" means "bow", as in "archery"! Or, if you like silly little tricks for memory, try these, which I just made up: Circumference starts with a C, which is curved; it means the curved part of the picture, the circle itself. Diameter starts with a D, which looks like half a circle; the straight line on the left is the diameter. Radius ... well, the slanted straight line of the R goes out from the middle like a radius. And a chord is any line in a circle that isn't special! If you have any further questions, feel free to write back. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
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