It is frequently measured using a device called a capillary viscometer - basically a graduated can with a narrow tube at the bottom. Kinematic viscosity is a measure of the resistive flow of a fluid under the influence of gravity. The other quantity called kinematic viscosity (represented by the Greek letter ν "nu") is the ratio of the viscosity of a fluid to its density. The quantity defined above is sometimes called dynamic viscosity, absolute viscosity, or simple viscosity to distinguish it from the other quantity, but is usually just called viscosity. There are actually two quantities that are called viscosity. Ten poise equal one pascal second making the centipoise and millipascal second identical. The most common unit of viscosity is the dyne second per square centimeter, which is given the name poise after the French physiologist Jean Poiseuille (1799–1869). The pascal second is more rare than it should be in scientific and technical writing today.
Despite its self-proclaimed title as an international system, the International System of Units has had little international impact on viscosity. The SI unit of viscosity is the pascal second, which has no special name. Or if you prefer calculus symbols (and who doesn't)… F The similarity to Newton's second law of motion ( F = ma) should be apparent. The more usual form of this relationship, called Newton's equation, states that the resulting shear of a fluid is directly proportional to the force applied and inversely proportional to its viscosity. (dynamic) viscosityįormally, viscosity (represented by the symbol η "eta") is the ratio of the shearing stress ( F/ A) to the velocity gradient ( ∆ v x/∆ y or dv x/ dy) in a fluid. Fluids resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them. Both Dynamic viscosity and Kinematic viscosity are interchangeable using following formula.Informally, viscosity is the quantity that describes a fluid's resistance to flow.The kinematic viscosity is referred as diffisivity of momentum.Water at 20 degree C has kinematic viscosity of about 1 cSt.It can also be reported in Centistoke (cSt) or m 2/s. The cgs physical unit for kinematic viscosity if stokes(St).Time taken is being noted and converted to kinematic viscosity.It is usually measured by noting down the time taken for fluid sample to travel throughĪn orifice in a capillary under force of gravity.The commonly used unit is Poise or Centipoise (i.e. ➤ Dynamic Viscosity (μ) = Shear Stress/Velocity Gradient It can also be defined as fluid's resistance to deform when subjected to force.It is defined as fluid's resistance to flow.There are two methods to measure viscosity of a fluid viz.ĭynamic viscosity and kinematic viscosity.Viscosity can be defined as measurement of fluid internal resistance to flow at.Viscosity of gases increases with increase in the temperature.Viscosity of liquids decreases with increase in the temperature.Viscosity: It is the inherent property of fluid which offers resistance to the flow.This page compares Dynamic Viscosity vs Kinematic Viscosity and mentions difference between Dynamic Viscosity and Kinematic Viscosity. Dynamic Viscosity vs Kinematic Viscosity | Difference between Dynamic Viscosity and Kinematic Viscosity
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