Drinking bird

  Drinking birds are thermodynamically powered toy heat engines that mimick the motions of a bird drinking from a fountain or other water source. They are also known as happy, dippy, dipping, tippy, tipping, sippy, sipping, dip-dip, dinking, or dunking birds.

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Construction and materials

A drinking bird consists of two glass bulbs, joined by a tube (the bird's neck). The tube extends nearly all the way into the bottom bulb but does not extend into the top. The space inside is typically filled with coloured dichloromethane (also known as methylene chloride).

Air is removed from the apparatus, so the space inside the body is filled by dichloromethane vapour. The upper bulb has a "beak" attached, which along with the head, is covered in a felt-like material. The bird is typically decorated with paper eyes, a blue top hat (plastic) and a single green tail feather. The whole setup is pivoted on a variable point on the neck.

Despite its classification and appearance as a toy, there are safety considerations. Early models were often filled with highly flammable substances. New versions alleviate this concern by employing dichloromethane, which is nonflammable. However, it can irritate the skin and lungs and is a mutagen and teratogen and is potentially a carcinogen. This does not render the bird unsafe, but owners should exercise caution not to break the toy, especially when displaying it near children and animals.

Physical and chemical principles

The drinking bird is an interesting exhibition of several physical laws and is therefore a staple of basic chemistry and physics education. These include:

• The combined gas law, which establishes a proportional relationship between temperature and pressure exerted by a gas in a constant volume.
• The ideal gas law, which establishes a proportional relationship between number of gas particles and pressure in a constant volume.
• The Maxwell-Boltzmann distribution, which establishes that molecules in a given space at a given temperature vary in energy level, and therefore can exist in multiple phases (solid/liquid/gas) at a single temperature.
• Heat of vaporization (or condensation), which establishes that substances absorb (give off) heat when changing state at a constant temperature.
• Torque and center of mass
• Capillary action of the wicking felt.

How it works

The drinking bird is basically a heat engine that exploits a temperature differential to convert heat energy to kinetic energy and perform mechanical work. Like all heat engines, the drinking bird works through a thermodynamic cycle. The initial state of the system is a bird with a wet head oriented vertically with an initial oscillation on its pivot.

The cycle operates as follows:

1. The water evaporates from the head (Maxwell-Boltzmann distribution)
2. Evaporation lowers the temperature of the glass head (heat of vaporization)
3. The temperature drop causes some of the dichloromethane vapor in the head to condense
4. The lower temperature and condensation together cause the pressure to drop in the head (ideal gas law)
5. The pressure differential between the head and base causes the liquid to be pushed up from the base.
6. As liquid flows into the head, the bird becomes top heavy and tips over during its oscillations.
7. When the bird tips over, the bottom end of the neck tube rises above the surface of the liquid.
8. A bubble of vapor rises up the tube through this gap, displacing liquid as it goes
9. Liquid flows back to the bottom bulb, and vapor pressure equalizes between the top and bottom bulbs
10. The weight of the liquid in the bottom bulb restores the bird to its vertical position

If a glass of water is placed so that the beak dips into it on its descent, the bird will continue to absorb water and the cycle will continue as long as there is enough water in the glass to keep the head wet. However, the bird will continue to dip even without a source of water, as long as the head is wet, or as long as a temperature differential is maintained between the head and body. This differential can be generated without evaporative cooling in the head -- for instance, a heat source directed at the bottom bulb will create a pressure differential between top and bottom that will drive the engine. The ultimate source of energy is a heat differential in the surrounding environment -- the toy is not a perpetual motion machine.

A recent analysis ^[1] showed that the evaporative heat flux driving a small bird was about 0.5 W, where as the mechanical power expressed in its motion was about 50 microwatts, or a total system efficiency of about 0.01%. More practically, about 1 microwatt can be extracted from the bird, either with a coil/magnet or a ratchet used to winch paperclips.

History

The drinking bird was invented by Miles V. Sullivan in 1945 and patented in 1946. He was a Ph.D. inventor-scientist at Bell labs in Murray Hill, NJ, USA.

The drinking bird in popular culture

The bird was an instant hit upon its creation and achieved near iconic status. It has even appeared in the American TV show The Simpsons, in the episodes "Brother Can You Spare Two Dimes?" "King-Size Homer", and "Das Bus". In the foremost episode, the drinking bird is used by Homer's half-brother Herb Powell as an example of a great invention. However, when Herb begins to talk about his own invention, Homer is still mesmerised by the bird and even offers to buy it from him. In the latter episode, Homer uses the drinking bird to operate the Y key (for "yes") on his work-at-home computer that controlled the necessary venting of gas for the nuclear power plant. Unfortunately, Homer neglects to check on the bird and it falls over, creating a critical situation in the area under Homer's control. In Das Bus, it is seen on Homer's desktop, and is snapped later in the episode.

A drinking bird also appears in the 1951 Merrie Melodies cartoon "Putty Tat Trouble". Tweety Bird spies one "drinking" from a glass and, mistaking it for a real bird, asks if he can join it. Tweety mistakes the toy's bobbing motion for a nod of assent and joins it, imitating its back-and-forth movement exactly. Shortly, Sam, another cat who is fighting with Sylvester over Tweety, swallows the drinking bird by mistake, and his body then uncontrollably mimics the same bobbing motion.

A drinking bird appears in the futuristic Woody Allen film "Sleeper".

Two drinking birds can be seen on the communal table aboard the space freighter Nostromo during the opening scenes of the 1979 science fiction film "Alien", directed by Ridley Scott.

In the 1990 film Darkman, drinking birds are used to set off explosions - one in Westlake's lab, and the other in a warehouse.

The drinking bird (under the name "water bird") is a furniture item in the Animal Crossing videogames. It also appears as the "dunkin' dragon" in the Sierra game Quest for Glory I, and it makes an appearance in the Gremlin Interactive game Normality.

On Jimmy Neutron, a drinking bird appears as a gift to Carl from the aliens.

See also

• Heat engine
• Thermodynamics