Data : d = 0.4 mm, η = 0.1 Pa.s, ρL = 0.9 × 103 kg/m3 = 900 kg/m3 , ρair = 1.29 kg/m3 , g = 9.8 m/s2.
Since the density of air is less than that of oil, the air bubble will rise up through the liquid. Hence, the viscous force is downward. At terminal velocity, this downward viscous force is equal in magnitude to the net upward force. Viscous force = buoyant force – gravitational force