Question

A spherical bubble is trapped inside a liquid of density ρ₁ ; coefficient of viscosity η. The bubble starts rising upwards. Besides the bouyant force; the following forces act on it.

(1) Only force of gravity

(2) The force due to gravity and the force due to pressure of liquid

(3) The force due to gravity; the force due to the pressure of the liquid and the force due to viscosity of liquid

(4) The force due to gravity and the force due to viscosity of the liquid

Answer 1

As bubble moves up the bouyant force on it is due to the difference of liquid pressure at the liquid layer just in contact with the upper and lower of the bubble. 

The other forces on bubble are: 

(1) force of gravity and 

(2) the viscous force of the liquid