Vortex

What to do: Turn the knob until you generate a vortex in the water column
What to notice: In fluid dynamics, a vortex is a region in a fluid in which the flow is rotating around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in phenomena such as smoke rings, whirlpools in the wake of boat, or the winds surrounding a tornado or dust devil. In most vortices, the fluid flow velocity is greatest next to its axis and decreases in inverse proportion to the distance from the axis.