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Viscous

Viscous is a property of fluids that describes their resistance to gradual deformation by shear or tensile stress. It reflects internal friction between adjacent layers as they slide past one another. A highly viscous fluid flows slowly and yields a thick, sticky consistency; a low-viscosity fluid, such as water, flows readily.

Viscosity is the measure of that resistance. Dynamic viscosity, denoted mu, quotes the shear stress required

Viscosity depends on temperature and composition. For most liquids, increasing temperature lowers viscosity. For gases, viscosity

Kinematic viscosity nu = mu / rho, with units of square meters per second, relates viscous effects to

In physics, viscosity appears in the Navier-Stokes equations as a viscous stress term, governing dissipation and

to
produce
a
given
rate
of
shear.
Newtonian
fluids
have
a
constant
mu
independent
of
shear
rate,
while
non-Newtonian
fluids
change
mu
with
shear
rate
or
time.
Viscosity
is
expressed
in
units
of
pascal-seconds
(Pa·s)
or
poise
(P),
with
1
P
=
0.1
Pa·s.
tends
to
rise
with
temperature.
Impurities,
molecular
structure,
and
phase
state
also
affect
viscosity.
density.
It
is
commonly
used
in
characterizing
flow
in
pipes
and
channels.
Practical
measurement
uses
viscometers
or
rheometers.
damping
of
motion.
In
engineering
and
industry,
viscous
fluids
influence
lubrication,
hydraulics,
ink
and
paint
spreading,
food
texture,
and
biomedical
contexts
involving
mucus
or
synovial
fluid.