Viscous drag force depends on ...........

Water is flowing steadily in a river. $A$ and $B$ are two layers of water at heights $40 \ cm$ and $90 \ cm$ from the bottom. The velocity of layer $A$ is $12 \ cm/s$. If the velocity of the water at the bottom is $0$,what is the velocity of layer $B$ (in $cm/s$)?

Define the coefficient of viscosity.

$A$ metal block of base area $0.20\,m^2$ is placed on a table,as shown in the figure. $A$ liquid film of thickness $0.25\,mm$ is inserted between the block and the table. The block is pushed by a horizontal force of $0.1\,N$ and moves with a constant speed. If the viscosity of the liquid is $5.0 \times 10^{-3} \,Pa-s$,the speed of the block is $.........\times 10^{-3}\,m/s$.

When stirring with a spoon is stopped in milk,it comes to rest after some time. Why?

The coefficient of viscosity for hot air is