"Drinking Duck"

Experimental setup of the drinking bird

• If you want to carry out the drinking duck experiment, you primarily need a glass hollow body with a neck and belly, the upper end becoming a duck's head with a beak, while the lower end of the glass tube neck descends into the belly protrudes.
• There must now be a liquid in the duck's belly that has a particularly low boiling point. In most cases, ether is used because the organic liquid fulfills the required properties particularly well. The glass neck tube should finally extend into the ether.
• It is particularly important for the attempt to secure the bird on a frame that enables it to tip over forwards. To do this, there must be an axis of rotation above the duck belly, over which the body can eventually tilt.
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• A glass of water is placed in front of the duck, the bird touching the water with its beak if it tilts forward far enough. This experimental set-up leads to the duck nodding incessantly. As long as there is enough water in the glass, the bird will never seem to stop nodding.

The physics behind the drinking duck

Several processes take place in the drinking duck, the sum of which ultimately leads to the bird becoming a kind of nodding perpetual motion machine.

1. You can already see the first process with the naked eye. So the ether column rises in the glass neck of the duck. The phenomenon behind this is evaporation. The ether evaporates at room temperature and the pressure in the duck belly rises, so that the ether is pushed higher and higher into the throat over time.
2. The fact that the bird finally begins to nod has to do with the subsequent shift in focus. In the initial state, the center of gravity is below the axis of rotation, but now it slips upwards and the bird nods forward until it hits the water. Its beak becomes moist to wet and the phenomenon of evaporation occurs again.
3. Evaporation from the beak removes heat from the glass bird's head. This in turn leads to a condensation of the ether in exactly that area, which in turn causes the pressure to rise.
4. At the bottom the glass bird's neck tube has already moved out of the ether due to the tilting movement. The increasing pressure can therefore be compensated because the tube is open at the bottom. Cold ether now flows through the neck tube into the duck's glass belly so that it returns to its original position.

• The nod continues in the described way, apparently indefinitely, because it is driven by the warmth of the environment. The ambient heat is used as drive energy. But the fact is that the drinking duck is not a true perpetual motion machine. Why? That can be illustrated with a connection attempt.
• The drinking duck uses the thermodynamic second law for itself: It wins hers energy from the increasing entropy, should mean from the increasing phase space volume, which results in the evaporation of the water. However, the increase in phase space volume is not unlimited. If the system is closed, the phase space volume is also limited and the pitching duck soon becomes stop nodding, because the phase space can no longer enlarge and energy production comes to an end comes.
• You can prove that fact by putting a bell jar over the bird and water glass. In this closed room, the humidity reaches a value of 100 percent over time, the evaporation stops and with it the nodding of the drinking duck. If you free the bird again, it will be able to nod again without any problems.