The Wittgenstein Rod

Instructions:

1.) Move the red point to determine the fixed pivot point.
2.) If we move the point on the circle, what shape will be formed?
3.) Try moving the point. What shape was formed?
3.) Repeat 1-3 several times for different positions of the fixed point.




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The Wittgenstein rod is a thought experiment proposed by Ludwig Wittgenstein. The problem is as follows: One end of a rod is attached to a circular track.  The rod passes through a fixed pivot point (the red point).  As one end of the rod traces the circle, what is the shape traced by the other end (the green point)?