| MadSci Network: Physics |
Actually, this is a very well-known little physics demonstration. It is an example of a heat engine. For considerable info on how it works, as well as some references, check the following links:
http://www.public.iastate.edu/~physics/sci.physics/faqold/dippy_bird.html http://www.exploratorium.edu/wsw/progress_snacks/dippingbird
Going to your favorite Internet search engine and searching on "drinking bird physics" or "dippy bird physics" will likely return more information than you care to have!
Very basically, the reason the thing works is that the evaporation of water at the head causes the head to cool when compared with the body. This in turn causes the vapor inside the head to condense, which causes a drop in pressure, which causes the liquid in the tube to rise, thus changing the center of balance and causing the bird to dip forward. The condensed fluid in the head then falls out, and it tips back up. See the links for more details.
The dippy bird most definitely does NOT violate energy conservation. The energy reservoir to drive the thing is the heat in the surrounding air, and gravity, in some sense.
Try the links in the MadSci Library for more information on Physics.