The force of viscosity is

The viscous force acting between the two layers of a liquid is given by,

$\frac{F}{A}=-\mathrm{\eta }\frac{\mathrm{d}v}{\mathrm{d}z}$

This $\frac{F}{A}$ may be called

A spherical ball is dropped in a long column of a viscous liquid. The speed of the ball as a function of time may be best represented by graph

A student plots a graph from his readings on the determination of Young's modulus of a metal wire but forgets to put the labels. The quantities on the $X$- and $Y$-axes may be, respectively,

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