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. Informally, viscosity is the quantity that describes a fluid's resistance to flow.

Viscosity index formula equation