Off on a Tangent
Click Go. The turtle acts somewhat like the LEGO robot. TOWARDS SUN points the turtle towards the sun at the center of the screen. After turning right 90 degrees, the turtle's left side is pointed toward the center, as if it had a sensor on its side. (RT is short for RIGHT; FD is short for FORWARD.) The turtle tries to keep its heading perpendicular to the line between it and the center -- and ends up moving in a circle. The turtle is constantly pointed along one of the circle's tangents (even if you drag the turtle or the sun). There's a slight problem. The turtle tends to spiral outward. The reason: With each step along a tangent, the turtle moves a tiny bit further from the center. If you make the steps smaller, the resulting shape become more and more circular. This circle provides a way of thinking about the earth's movement around the sun. The sun's gravity "tries" to pull the earth inward. But the earth is moving perpendicular to the sun's pull. The sun doesn't succeed at pulling the earth any closer, but it succeeds at turning the earth's heading, keeping it always perpendicular to the sun's pull. Go to the next page or the previous page or the contents page. Mitchel Resnick and Brian Silverman Epistemology and Learning Group MIT Media Laboratory Last modified: 2/4/96 |