You will find very simple and "recreative" experiment about the generation of
a Vortex...You will see with this experiment how a bidirectional flow
(water/air) share the small 9 mm hole between the two plastic soda
bottles...Very amazing and instructive for the knowledge of vortexes.....
See at :
http://ourworld.compuserve.com/homepages/jlnaudin/html/vtxbottle.htm
Have fun,
Jean-Louis Naudin
04-08-98