A rod 150 mm in diameter moves along its axis at 0.15 m/s inside a concentric cylinder 150.4 mm in diameter and 1.10 m long. The space between them is filled with an oil of specific gravity 0.82 and kinematic viscosity v = 1 x10^-4 m^2 /s.
a) what is the viscous force resisting the motion?
b) If the viscous force were twice of that calculated in a) what would the rod speed be?

Afan that can provide air speeds up to 60 m/s is to be used in a low-speed wind tunnel with atmospheric air at 35 c. if one wishes to use the wind tunnel to study flat-plate boundary layer behavior up to reynolds numbes of re 10, what is the minimum plate length that should be used? at what distance from the leading edge would transition occur if the critical reynolds nurnber were rer,e = 5 × 105?