Pattern Formation in Periodically Forced Fluids
When a fluid is subject to a periodic forcing in the vertical direction, it may form spatio-temporal patterns. These patterns result from what is called the Faraday instability. The examples below are a collection of photos taken of a sinusoidally forced petri dish of water. The different patterns here are the result of varying the frequency and amplitude of the forcing.
Rocking Faraday
When a fluid is subject to a rocking motion, similar to that of a coin spinning down, then things can get more complicated. Rotating patterns, rings moving at different speeds, and even ratcheting can occur.
Quicktime movie of rotating patterns 
The Apparatus
