Wednesday, July 31, 2013

Shaking and Dancing

Since every bathroom in my house is de facto a "men's room," I got to thinking about a bit of doggerel that my father taught me long ago:
"No matter how hard you shake and you dance,
Those last drops won't fall out 'til you're wearing your pants."

Anyone who is still reading at this point loves me enough to trust me when I say, I think that it actually makes sense from a fluid mechanics standpoint!  The drop hangs from one's urethra initially, and keeps from falling due to inter-molecular forces (like surface tension) within the fluid.  These forces are stronger than the small gravitational effect on such a tiny mass.  Then, along come the undies and capillary action with adhesion!  The liquid happily transfers to the fabric.

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