is: the phenomenon of internal friction in a fluid, leading to energy dissipation and stresses due to distortion of fluid elements. [P2.3, P7.6]
arises microscopically: from the transport of molecular momentum between adjacent layers of fluid in relative motion. There is a net transport of momentum from regions of high momentum to regions of low momentum, this tends to reduce the momentum difference between the layers and therefore the relative motion. [P7.5]
is therefore: a transport process.
is also: an abbreviation for the coefficient of viscosity, which is a measure of the difficulty with which a fluid flows (higher for treacle and motor oil than for water). [P5.2]
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