What is inertial force in the context of fluid dynamics?

Under a pressure head,the rate of orderly volume flow of a liquid through a capillary tube is $Q$. If the length of the capillary tube is doubled and the diameter of the tube is halved,the rate of flow would become:

What is critical velocity? Write its equation.

In Poiseuille's method for the determination of the coefficient of viscosity,the physical quantity that requires the greatest accuracy in measurement is:

$A$ liquid is flowing in a horizontal uniform capillary tube under a constant pressure difference $P$. The value of pressure for which the rate of flow of the liquid is doubled when the radius and length both are doubled is

Water is conveyed through a uniform tube of $8 \text{ cm}$ in diameter and $3140 \text{ m}$ in length at the rate of $2 \times 10^{-3} \text{ m}^3/\text{s}$. The pressure required to maintain the flow is (Viscosity of water $= 10^{-3} \text{ SI units}$):