Friday, September 16, 2016

Bouncing Liquid Soap

If you pour liquid soap as a thin string onto a surface it will eventually make a puddle and then start to pile up, every so often instead of sticking, the streaming soap will shoot off at right angles or sometimes strait up into the air! This surprising behavior is the Kaye Effect, discovered in the 60's by Allen Kaye, it occurs in all shear thinning liquids, non-Newtonian fluids that become less viscous as you pour and stir them.

As the incoming stream impacts against the standing pool of soap, a very thin sheet of air is trapped in between. This sheet of air makes the standing pool act like a frictionless surface, the incoming stream slides away in all directions or makes a small divot which then acts like a ramp, directing the stream back up into the air! By using a syringe it is possible to fire a stream sideways across the surface of the soap where it then acts like a long, heavy chain thrown across a sheet of ice.

Another interesting behavior is when a kink or wave in the falling stream of soap remains stationary or travels backwards up the stream against the flow! (See 1m12s) This unusual event can also be seen in lengths of falling chain (or long loops of continuously flowing chain).

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