Cinderella is a commercially available 2-D geometry drawing program, very well suited to demonstrate geometrical principles and constructions. I use it to make JAVA applets to convey geometric algebra (even though it is not written in that language!) and useful constructions for Lego hobbyists.

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The first demo you start will take some time, since it needs to download the
421 kb jar-file containing the cinderella code that runs all examples. All demos
after that will start much more quickly.
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- Geometric algebra - specific
- line representation, by 2-blades (bivectors)
- intersection of lines, in 2-space
- separation of skew lines, by trivectors
- rotation composition , by multiplication of quaternions, visualized on the sphere of directions
- projection using a pinhole camera
- inverse of a vector
- inverse of a bivector
- projection onto a rotor
- composition of projections
- Eckhard Hitzer has many more Cinderella/GA demos in the same vein.

- Fun geometry
- 5-circle theorem, and a nice little pentagon puzzle
- Simson's theorem, about the special nature of a circumcircle
- touching-circle theorem, using inversive geometry
- Snell's law, by construction.

- Linkages
- 4-bar linkage, the primal linkage
- 8-bar linkage, how to get a piano on stage
- dwell mechanism
- Peaucellier cell, to convert between rotary and linear motion
- walking beams, how to power a Norwegian mine on top of a mountain using water at the bottom

Leo Dorst 20020626