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Physics in the kitchen sink



Did you notice that some bottles contain less wine than you might think?
Their bottoms are not flat. The same is true for a plastic dish in which
pitted dates from the Coachella Valley Date Company are sold. No, I am
not advertising their product, or complaining about the deceiving display
of the 1 LB of dates. It is a nice container (depth=5 cm, diameter=15 cm,
the bottom indentation large enough to hide an egg) for some demos.

Use a pointy knife or pencil, to support the open dish (be placing the
pointy end at the center of the indentation). You have a steady equilibrium.
Spin the dish; it turns for a long time. While the dish is spinning hit it
with a spoon. A cheap way to demonstrate precession. But that is not what
prompted me to type this message.

The dish is not spinning. Slowly pour some water into it from a faucet. A
very small amount of water will disequilibrate the system. Now try to pour
water while the dish is spinning. You will see that about five times as much
water is needed to destroy the equilibrium. Any comments on this (entropy or
otherwise)? The shape of the bottom resembles a mold for a cake, or for a
doughnut. The swirling ripples, not very deep, make the clock-wise rotation
different from the couner-clock-wise.
Ludwik Kowalski