Rolling One Parabola on Another

Requires a Wolfram Notebook System
Interact on desktop, mobile and cloud with the free Wolfram Player or other Wolfram Language products.
The focus of a parabola that rolls around another fixed identical parabola describes a straight line, which is the directrix of the fixed parabola.
Contributed by: Izidor Hafner (August 2012)
Open content licensed under CC BY-NC-SA
Snapshots
Details
Reference
[1] J. Bryant and C. Sangwin, How Round Is Your Circle?: Where Engineering and Mathematics Meet, Princeton, NJ: Princeton University Press, 2008, pp. 44–45.
Permanent Citation
"Rolling One Parabola on Another"
http://demonstrations.wolfram.com/RollingOneParabolaOnAnother/
Wolfram Demonstrations Project
Published: August 15 2012