Points off a rolling wheel make traces. What makes those traces have symmetry?
In the diagram the point P' can move to different places along the dotted line. Each position P' takes will fix a corresponding position for P. If P' moves along a straight line what does P do ?
A cheap and simple toy with lots of mathematics. Can you interpret the images that are produced? Can you predict the pattern that will be produced using different wheels?
Locus problems that have elegant visual simplicity readily draw us into geometric reasoning because the pleasure of seeing what is going on is accessible.
This problem uses a mapping called Inversion Geometry which has wide application and works well as an aesthetically satisfying introduction to the concept of mapping.