Does perpetual motion machine really exist? I recently saw a video on Youtube about a perpetual motion machine. Here is the link:
http://www.youtube.com/watch?v=OS1KXMsE2qk
It's on Robert Boyle's flask.
Where does the energy come from?
 A: I was surprised to see an effect that's actually real, and not a hidden motor or something like that.  I believe this experiment can feasibly be repeated.  The principles behind it make sense.
The driving force comes from the density difference in the cup versus in the pipes.  The cup has very few bubbles in it compared to the pipe.  Why?  Because:


*

*The bubbles in the cup have an exit strategy - floating to the top.  Not so in the pipe.

*The pipe has greater wall area to volume ratio.  So it likely has more nucleation sites for the bubbles.


If I were recreating this, I would design the pipe to turn horizontal/vertical as close as possible to the bottom of the cup, in order to help maximize the driving pressure.  Also, make sure to use the soda/beer right after opening it.
This experiment shows (not perpetual motion) that carbonation contains stored energy in some sense.  More specifically, the process of a carbonated drink decaying into un-carbonated liquid and CO2 gas liberates extra energy.  A small fraction of that energy is harvested here to drive the flow.
Very good science project.
In order to demonstrate that it is not perpetual motion, either allow it to run to its full conclusion, or try it again with soda that has sat out for a day.  The data should support the hypothesis that the driving force to power the flow comes from stored energy in the carbonation.
