With a wave, water is displaced a short distance as the wave travels. Think of loose sping, (e.g. a slinky spring) and how if you stretched it out a bit a compr

With a wave, water is displaced a short distance as the wave travels. Think of loose sping, (e.g. a slinky spring) and how if you stretched it out a bit a compression wave would travels down it[1]. Each part of the spring moves only a little, but the wave travels the length of the spring. With a vortex the material spinning in the vortex stays together, that's why the dye droped into the vortex stays in the vortex and you would see it travel across the pool, and you see smoke rings travel through the air. [1] http://www.youtube.com/watch?v=rd3afUct2l8 http://www.youtube.com/watch?v=rd3afUct2l8