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by JoeAltmaier 1526 days ago
Reframe the system to the moving water. The fish is then swimming upstream.

All frames of reference are valid. So yes, perpetual motion.
2 comments
PeterisP 1526 days ago
Reframe the system to the moving water and put a watermill or a hydroelectric power plant in there in there - perpetual motion and extracting energy. A flowing river is not a closed system.
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plutonorm 1526 days ago
what about sailing up wind?
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