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Clever Cones/Classic Circles
(Geometry/Dimension)
By Carol Peterson
Dimension (di-MEN-shun) means a measure in one direction. Some shapes are 2-dimensional and some are 3-dimensional. A 2-dimensional shape has height and width—meaning it is tall and wide. A 3-dimensional shape has height and width, too. It also has depth. An example of a 2-dimensional shape is a circle drawn on a paper. The circle is tall and wide, but it is not deep because it does not extend up above or beneath the paper. But a sphere—a ball, for example—is 3-dimensional. It is tall and wide and also deep.
How do you draw a circle? One way is to trace around something that is round. For example you can place a soup can on a sheet of paper, hold it in place and draw around it, following the can edge with the pencil. When you remove the can, you are left with a drawing of a circle.
You can also use a compass; not a magnetic compass that tells direction, but a drawing instrument compass. It has 2 legs, one with a point and one with a clamp to hold a pencil.
You open the legs half as wide as you want your circle to be. Then you place the pointed end on the paper, hold it in place, and swing the pencil end around the pointed end in a circle, with the tip of the pencil touching the paper. When you remove the compass from the paper, you have drawn a circle.
You can also attach a pencil to one end of a string and a tack to the other end of the string. Insert the tack into the paper. Holding, the string tight and with the tip of the pencil touching the paper, swing the pencil around in a circle, with the tack as the middle point. When you remove the string, the pencil, and the tack, you have drawn a circle.
A circle is a flat figure. It is 2-dimensional. You can see the shape of the circle on the paper, but it doesn’t have any depth. It does not stand up above the paper. It can represent the 3-dimensional shape of a sphere.
A cone is also a 3-dimensional figure. To create a cone you could draw a circle and cut it in half. Then cut out the half-circle shape and join the 2 halves of the straight edges together so that the curved edge of the half circle makes the bottom of the cone. If you wanted to draw the shape of the 3-dimensional cone on paper, you would draw it as a triangle with one side of the triangle as a curve.
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