Problem 2.244

Two identical parallel discs have a common axis and are located at a distance $h$ from each other. The radius of each disc is equal to $a,$ with $a \gg h .$ One disc is rotated with a low angular velocity $\omega$ relative to the other, stationary, disc. Find the moment of friction forces acting on the stationary disc if the viscosity coefficient of the gas between the discs is equal to $\eta$.