PURPOSE: To show that "permanent" spiral structure can exist as a wave which moves independently from the fluid, and the winding-up consequence of spiral structure fixed to the fluid.

DESCRIPTION: Rapidly rotate the stirrer to produce a vortex, making the direction of rotation clear to the class. Spiral waves will then be seen initially rotating very slowly with the fluid, then stopping, and finally rotating in the opposite direction. Finally, by injecting food coloring in a line across the vortex it can clearly be seen that differential rotation would destroy the spiral structure if it were "fixed" to the fluid.

SUGGESTIONS: The circular insert is used inside the Coriolis tank to minimize reflected waves.

REFERENCES: (PIRA unavailable.)

EQUIPMENT: Square plastic tank with circular insert, three inches of water, food coloring, and overhead projector.

SETUP TIME: 10 min.

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