If liquid helium can flow forever, isn't this perpetual motion?

Well...not really, because even liquid helium atoms have some small amount of thermal agitation since they are at a temperature of a few degrees above absolute zero. There will always be some slight friction, however small, between one collection of atoms in the superfluid, and the surface it is in contact with. This will eventually bring the liquid to rest, though it may take longer than the lifetime of the superfluid. The superfluid absorbs the frictional heat from the encounter, and rapidly boils off this energy in the form of atoms which have energies above the vapor point of the liquid.


Copyright 1997 Dr. Sten Odenwald
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