Dippy Duck

Repetitive Motion that is not Harmonic

How it works:
Dippy Duck is a small heat engine, consisting of a barbell of glass with the top bell a simple sphere with flocking, and the bottom sphere with the bar tube extending into it to just above the bottom.

The bar is held by a knife edge clamp at its middle, which then sits in a pair of V 's at the top of a stand made to look like legs.

A liquid with a high vapor pressure almost fills the bottom sphere. If the flocking on top of the duck is wet, then evaporative cooling reduces the pressure in the top of the barbell, and the liquid rises in the tube.

The liquid has to be warmer than room temperature for the duck to work. Get it warm before with hands, or in the case of a flock of dippy ducks, use a spotlight to add some radiant heat.

As the liquid rises in the tube it changes the center of gravity, so the oscillations with which the duck is started increase in amplitude and slow down, until the balance is over and the top sphere touches water in a beaker, rewetting the flocking. The duck pauses with the bar almost level, which allows the high pressure in the bottom to equalize with the top, and the liquid flows back to the bottom, which eventually causes the balance to revert to vertical. The duck returns to its original position, rocking as the liquid slowly rises in the tube, until it falls forward again and repeats.

Comments:
Once there was a dippy duck over a foot tall, gone now and no apparent replacements on the market. A dozen ducks each six inches tall goes a certain distance.

Drinking Bird website will fill in the details to an almost painful degree.