where η is the constant of proportionality and is called the absolute viscosity, r is the radial distance form the central axis of the pipe, and dv/dr is the velocity gradient normal to...where η is the constant of proportionality and is called the absolute viscosity, r is the radial distance form the central axis of the pipe, and dv/dr is the velocity gradient normal to the flow. He was able to characterize the transition between these two types of flow by a parameter called the Reynolds number that depends on the average velocity of the fluid in the pipe, the diameter, and the viscosity of the fluid.
