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Re: [Phys-L] Impossible vehicles.

Good to see David Bowman  refers to Don Simanek's web site.

 Don is conspicuously absent from Phys-L these days, perhaps on account of his years - a handful more than mine even! Don's entertaining materials on perpetuum mobiles feature several off-balanced wheels mostly featuring swinging weights or sliding chains.It reminds of such a moving wheel once on view at the Museum of Science & Industry (Birmingham) - since moved.
This perpetual motion differed from most in having a small gas flame bearing on the wheel rim at one side turning slowly on a horizontal axis, and a fixed magnet in that location. This jeu d'esprit emanated from the Chemistry Dept of Birmingham U. at a time when humor was perhaps more valued in akademe. You will appreciate that this constituted a heat engine, no more.
David's boat on a river in still air moving up or downstream faster than the water speed seems to be less reliable in concept because it demands a connection both to stream flow and immobile bed (mud?) or bank, but still it is in the spirit of the land-yacht or directly upwind boat. On Thursday, June 3, 2021, 07:45:59 AM CDT, David Bowman <> wrote:


The physics of sailing upwind is the same as sailing downwind faster than
the wind.
This is discussed in some detail, using a couple of different approaches, at

Some useful diagrams are included.

JD's discussion in his above link and the Donald E. Simanek reference therein are quite valuable.  Of course a cute implication of all this is it's quite possible to sail both upstream in a river in perfectly calm air (relative to the ground), and to sail downstream faster than the current in the same calm conditions.  The first situation is a form of sailing downwind faster than the wind, and the 2nd is a form of sailing directly upwind.

David Bowman
Forum for Physics Educators