From my Martian Math curriculum:

http://www.4dsolutions.net/ocn/python/movingballs.py http://www.4dsolutions.net/ocn/python/movingballs2.py http://www.4dsolutions.net/ocn/python/movingarrows.py This one is especially likely to crash your VPython, if your video card isn't running the latest something-or-other, read all about it under Visual 5 (vpython.org). I had to upgrade my desktop driver, laptop no problemo, high end Apples in the classroom no problemo either. http://www.4dsolutions.net/ocn/python/movingletters.py Kirby re Martian Math: http://bfi.org/news-events/community-content/martian-math-and-synergetics