Drinking bird

A drinking bird (also known as " Wippvogel ", " Pick bird ", " boozer ", " Nick Duck ," " Nick Bird " or " glass -crested Pochard ," engl. "Drinking bird" ) is a physical toy.

Construction

The drinking bird is usually constructed as a hollow body made ​​of glass, consisting of a neck in a filzüberzogenen head goes up with beak and extends down into a (completed) stomach, which without air having a low boiling point liquid in the vicinity of room temperature (eg, ether) is filled. The bird is situated on a frame and can tilt around an axis of rotation above the abdomen to the front. He tilts far enough forward so extends his beak into standing before him water glass.

Operation

The water on the wet beak evaporates into the atmosphere. The necessary heat is removed from the glass head. Due to the resulting evaporative cooling cools next to the glass head and condenses and the ether vapor in the head. This here decreases the vapor pressure. The vapor in the lower part of the body can now expand and pushes the colored liquid in the glass tube to the top. Thus the center of gravity and the bird stands unstable and tipping forward in the inclined position. At the same time the lower end of the tube out of the liquid in the abdomen moves out by the inclination, so that pressure equalization can take place. This colder liquid flows back into the abdomen and warmer vapor rises into the head that tilts bird back to the starting position. He commutes to the starting position and the process begins again. If you spend just an automatic water replenishment, can "forever" nod of the bird. Thus, it is a heat engine having a cyclic process. The selected fluid must be readily vaporize at room temperature. Her saturation vapor pressure must be sensitive to the temperature rise. Ether would be suitable, but is combustible, dichloromethane is harmful to the environment, so it is a secret colored mixtures.

Variants

If the drinking glass filled with alcohol, the bird is drinking more often because it evaporates easily. The tilting movement can also be triggered by a specific heating of the lower body with a hair dryer or heat radiation.

Physical concepts and laws that will be addressed with the toy: Ideal gas, saturation vapor pressure, vapor - liquid equilibrium, the Clausius- Clapeyron equation, heat of evaporation, condensation, gravity, torque, capillarity, 2nd law of thermodynamics.

The drinking bird is apparently a perpetual motion machine of the second kind, since it wins its driving energy from the ambient heat and can thus produce by lowering the outside temperature kinetic energy.

In reality, however, he met the second law of thermodynamics, since it gets its energy from the increase in entropy, which takes place when the water evaporates from the glass to the beak and mixes with the air.

In a closed system, the relative humidity reaches 100 % soon and the cooling evaporation process comes to a halt. This is easy to show by a put over the bird bell jar: after a few minutes, the movement comes to a halt. Removing the bell, the movement of the bird starts again.