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 ......... $s^{-1}$.

$A$ Newtonian fluid fills the clearance between a shaft and a sleeve. When a force of $800$ $N$ is applied to the shaft,parallel to the sleeve,the shaft attains a speed of $1.5$ $cm/s$. If a force of $2.4$ $kN$ is applied instead,the shaft would move with a speed of ......... $cm/s$.

The flow of water in a river at the banks is slower than at the middle of the river. Explain.

Discuss the coefficient of viscosity in terms of stress and strain.

$A$ cubical block of side $a$ and density $\rho$ slides over a fixed inclined plane with constant velocity $v$. There is a thin film of viscous fluid of thickness $t$ between the plane and the block. If the angle of inclination is $37^{\circ}$,then the coefficient of viscosity of the thin film will be:

$A$ good lubricant should have