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Flying Circles

When you fly over the Midwest in the United States, you sometimes see large circular patterns in the fields. The circles seem to be several hundred feet in diameter. It is tempting to think that these circles are artifacts of visits from ancient astronauts. But there is a simpler (if less romantic) explanation.

Since circles are such precise figures (it is very difficult to draw a circle by hand), you might not expect to see many circles in the world. But the world is full of circles: the ring left by a glass on the table, the ripple from a stone thrown into a pond, the bottom of a tin can, the cross-section of a soap bubble, the face of a watch -- and the circles in farm fields.


Why all these circles? In each case, think carefully about the materials, the function, and the history of the object. The story is somewhat different in each case.

As for the circles in the Midwest, the story is quite simple. The irrigation equipment tells the story. There is a long horizontal pipe with one end on wheels and the other end on a rotating joint. As the pipe pivots, water drips out of the pipe. The result is a circle, with the rotating joint at the center.

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Mitchel Resnick and Brian Silverman
Epistemology and Learning Group
MIT Media Laboratory

Last modified: November 17, 2003
by Rupert Russell