Liquid flow velocity at a solid wall: (a) Empirical evidence shows that fluid = wall , for example, if the wall/surface is stationary and impermeable, u = v = w = 0; however, wall-velocity-slip may...

Liquid flow velocity at a solid wall: (a) Empirical evidence shows that fluid = wall , for example, if the wall/surface is stationary and impermeable, u = v = w = 0; however, wall-velocity-slip may occur; but when and why? (b) From the viewpoint of two reference frames, that is, one fixed on the ground and the other fixed to the moving object (say, an airplane), what is air in the two reference-frame cases, and what is air far away from the plane in both reference frames?