Viscosity is a peculiar property exhibited by the fluids due to which an internal frictional force comes into action when the fluid starts moving, and this very friction opposes the relative motion between the layers of the fluid. Viscosity is referred to as the ratio of the force required to make adjacent layers of the liquid move over each other. Furthermore, other abbreviations are sometimes used such as SUV (Saybolt universal viscosity) or SSU (Saybolt seconds universal). Earlier, the kinematic viscosity was measured by using Saybolt viscometer where the units were expressed in Saybolt universal seconds (SUS). Some non-standard units of viscosity are the Reyn which is a British unit of dynamic viscosity. Sometimes the unit centistokes (cSt) is also used.The cgs unit for kinematic viscosity is stoke (St) which was named after Irish mathematician and physicist Sir George Gabriel Stokes.It is also widely used in ASTM standards, as centipoise (cP).In the CGS standard, the unit of viscosity is poise (P) which is used in honor of a French physiologist Jean Léonard Marie Poiseuille.
The unit is generally called Decapoise or Poiseulle. In SI standards, the unit of \(\eta\) is Kg/ms, and Nsm -2. Now we can substitute the individual units and find the units in SI and CGS. Note: neglecting the negative sign for the sake of convenience.įrom the equation, we can determine the dimension of \(\eta\) as ML -1T -1. The coefficient of viscosity is regarded as the measure of viscosity, the unit of coefficient of viscosity is considered as the unit of viscosity. Key Terms: Viscosity, SI Unit, CGS Unit, Kinematic Viscosity, Dynamic Viscosity, Poise, Dimensional Formula, Poiseuille, Coefficient of Viscosity
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