The next time you're in the shower, try pouring a steady stream of shampoo into an open, flattened palm. See how the thread loops and buckles as it comes into contact with your hand? Physicists who study fluid dynamics call this behavior "the rope-coiling effect;" it's a physical property commonly observed in viscous fluids (like shampoo) when they're poured from a nozzle onto a flat surface (like your hand).

Now direct your attention to the video up top. In it, University of Toronto physicist Stephen Morris and his colleagues have replaced the crude conditions of your shower-laboratory with an apparatus capable of much greater experimental precision. Morris' viscous fluid is dispensed at a uniform rate from a nozzle positioned at a set height onto a much flatter surface than the palm of your hand. And to make things extra interesting, Morris and his colleagues have replaced the stationary surface of your palm with a motorized belt, the speed of which can be varied.

Advertisement

In doing so, Morris and his colleagues note that "the rotational symmetry of the buckling instability is broken, and a wealth of interesting states are observed." Fuck Yeah Fluid Dynamics walks us through the changes that we see in the video:

In this video a very viscous (but still Newtonian) fluid is falling in a stream onto a moving belt. Initially, the belt is moving quickly enough that the viscous stream creates a straight thread. As the belt is slowed, the stream begins to meander sinusoidally [i.e. in the pattern of a sin curve, pictured here] and ultimately begins to coil. Aside from some transient behavior when the speed of the belt is changed very quickly, the behavior of the thread is very consistent within a particular speed regime. This is indicative of a nonlinear dynamical system; each shift in behavior due to the changing speed of the belt is called a bifurcation and can be identified mathematically from the governing equation(s) of the system.

Beautiful stuff, right? Hooray for shower physics!

[arXiv via Fuck Yeah Fluid Dynamics]
Sinusoidal waveform via Wikimedia Commons