Q1: Which of the following is not a unit of kinematic viscosity ?

ANS:A - Poise

The unit "Poise" is not a unit of kinematic viscosity; it is a unit of dynamic viscosity. Kinematic viscosity is defined as the ratio of dynamic viscosity to density. Its units are derived from dividing the units of dynamic viscosity (e.g., poise or Pascal-second) by the units of density (e.g., grams per cubic centimeter or kilograms per cubic meter). Therefore, the unit "Poise" is not a unit of kinematic viscosity. The units of kinematic viscosity include square centimeters per second (cm²/s) and Stoke (St). So, the correct answer is "Poise". The Poise (P) is a unit of dynamic viscosity in the centimeter-gram-second (CGS) system of units. It is named after the French physiologist Jean Louis Marie Poiseuille. Dynamic viscosity, represented by the symbol η (eta), measures a fluid's resistance to flow under an applied force or stress. In simpler terms, it quantifies how "thick" or "sticky" a fluid is. The Poise is defined as the dynamic viscosity of a fluid with a shear stress of one dyne per square centimeter (1 dyne/cm²) when its velocity gradient is one reciprocal second (1 s^-1). Mathematically, dynamic viscosity (η) can be expressed in terms of force per unit area (stress) and rate of deformation (velocity gradient) as follows: 𝜂=stressvelocity gradientη=velocity gradientstress​ In the CGS system, the unit of force is the dyne, and the unit of velocity gradient is the reciprocal second (s^-1). Therefore, the unit of dynamic viscosity, the Poise, is expressed in dyne-second per square centimeter (dyne·s/cm²). For practical purposes, the centipoise (cP) is often used as a more convenient unit, where 1 Poise is equivalent to 100 centipoise (1 P = 100 cP). The Poise is commonly used in fluid mechanics, rheology, and viscosity measurements, particularly for fluids with relatively low viscosities, such as water, oils, and gases.