VORTEX STRETCHING AND TILTING
SIMPLE TOOLS FOR MECHANICAL DEMONSTRATION OF TILTING AND STRETCHING.
Orient tube and twist to show how a vortex tube may tilt and bend.
Swing ball. Vertically stretching the ends forces ball to a smaller radius causing spin up by conservation of angular momentum. Strings are mechanical analogue of mass conservation in an incompressible fluid (fluid move out the top and bottom => fluid must move in from the sides).