In the measurement of viscosity of liquids using terminal velocity experiment, spherical balls of same radius but having different densities are…

In the measurement of viscosity of liquids using terminal velocity experiment, spherical balls of same radius but having different densities are used. The variation of the terminal velocity $\displaystyle (v)$ with the ratio of density of spherical ball $\displaystyle (\sigma)$ to density of the liquid ( $\displaystyle \rho$ ), is best represented by :