Spinning in the Wind
One basic idea makes pinwheels and windmills work: the turbine. Here's how to make a simple one.
With scissors, cut a square out of a piece of thin cardboard. A piece from an index card or an empty box of tissues works well. The size is not important, but first try a square about one inch on each side.
Bend one corner toward you. Bend the opposite corner away from you. Now hold the square lightly, as shown to the right. You have made a turbine.
You can make it spin by blowing against it. You might have to blow on it several different ways before you discover how to make it work well. Try blowing against the side of it rather than the center.
You can use your turbine to make a changing picture. Make a turbine from a piece of index card or some other stiff paper that's plain on both sides. Mark an X in the center on one side. Mark a large O in the center of the other side. Now make it spin. When it is spinning fast, you will be able to see the O with an X inside of it.
Create your own changing pictures. For example, draw a face like the one in Figure A on one side of a turbine. Then flop the turbine over and hold it up to a light so you can see the face through the card. On the side facing you, draw three lines, like those in Figure B. Now make the card spin to see the face change.
How It Works
The corners are bent so that they catch the wind and the air always pushes the card around and around in the same direction. Turn the card upside down, and see which way it turns when you blow on it.
If the card turns fast enough, it can fool your eye just as a movie does. Your eye "remembers" each picture for a short period of time. If the pictures change fast enough, they add together to make an O with an X inside it--or to change a face completely when you make its head spin.
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