PhysProf wrote:One thing left out of the liquid helium section: when a superfluid (below 1.9K), it has zero viscosity. That will make it impossible to row your boat - the oars will slip through the LHe without any resistance at all. No resistance --> no force on oar, by Newton's 3rd law.
I'm not superfamiliar with superfluids, but something seems intuitively wrong about this, so maybe you can explain.
Zero viscosity means that it won't "stick" to its container or objects passing through it at all, and therefore won't have any friction as it flows through and around things. But certainly if you shot a high-velocity column of the stuff at something (like water out of a fire hose), that something would still get knocked back as the the molecules bounced off of it and changed direction, imparting their momentum into the target, yes? It wouldn't magically flow around anything you shot it at and pass by unfelt by the target?
If so, then you should still be able to paddle through a lake of the stuff. The lake won't "grab" the paddle at all, so you'll have less traction to push the fluid around, but you will still be deflecting molecules as you intersect the paddle with their direction of motion, changing that direction and the momentum of the paddle (and thus you and thus the boat you're sitting on) in the process, too.