The speed of the water in a river is $V$ near the surface. If the coefficient of viscosity of water is $\eta$ and the depth of the river is $H$, then the shearing stress between the horizontal layers of water is

The relative velocity of two consecutive layers is $8 \ cm/s$. If the perpendicular distance between the layers is $0.1 \ cm$,then the velocity gradient will be ......... $s^{-1}$.

$A$ thin square plate of side $2\ m$ is moving at the interface of two very viscous liquids of viscosities $\eta_1 = 1 \text{ poise}$ and $\eta_2 = 4 \text{ poise}$ respectively, as shown in the figure. Assume a linear velocity distribution in each fluid. The liquids are contained between two fixed plates. $h_1 + h_2 = 3\ m$. $A$ force $F$ is required to move the square plate with a uniform velocity $10\ m/s$ horizontally. The value of the minimum applied force will be ........ $N$.

Define the coefficient of viscosity.

The coefficient of viscosity of an ideal fluid is

What is viscous force? On what factors does viscous force depend?