Does air create a friction force on water? Would a gutter be much quicker at hav…

Does air create a friction force on water? Would a gutter be much quicker at having water flow through it, rather than a pipe?

Air does exert frictional forces on water, but much less than a surface would. Thus a gutter would be a better water carrier than a pipe. It would have one less surface to slow the flow of water.

Does super cooled helium act in a viscous or non-viscous manner?

Does super cooled helium act in a viscous or non-viscous manner?

Below 2.17 K, liquid helium behaves very differently than normal fluids. It behaves as though it were made of two intermingled fluids: one that is normal in every way and the other that is completely without viscosity. Depending on what sort of experiment you do, you will see one or the other fluid. If you swirl the liquid helium with a stick, you will see the viscous fluid component swirling and splashing. If you pour the liquid helium through a filter made of tightly packed dust, you will see the non-viscous component rushing through. No normal fluid can travel through packed dust, because its viscosity slows its travel until it doesn’t move at all. But the viscosity-free component of liquid helium can flow easily through any holes, no matter how small. It can flow through holes that even helium gas has trouble passing.