A fluid may be defined as a substance which deforms continuously
when subjected to a shear stress or in other words a fluid is a substance which
cannot withstand shear stress. Fluid mechanics deals with the behavior of
fluids at rest and in motion. Fluids may be of liquid or gaseous forms. Liquid
is practically incompressible and occupy definite volume and have free
surfaces. Whereas, gaseous fluids are compressible. Gases can expand until it
occupies all portion of any containing vessel.
Mass Density, ρ:
Properties of fluid:
Important fluid properties are mentioned below
Mass Density, ρ:
It
is the mass per unit volume. The density of water at standard temperature and
pressure is 1000 kg/m3 .
Specific volume Vs :
It
is the volume occupied by unit mass of fluid i.e. specific volume is the
reciprocal of density. Therefore, Vs = 1/ρ.
Specific weight, ɣ :
Specific
weight may be defined as the weight of a unit volume of a substance. For water
at standard conditions specific weight is equal to 9.81 kN/m3 . The
relation between specific weight and density can be written as ɣ = ρg.
Viscosity, µ:
Viscosity
may be defined as the property of a fluid which determines the amount of its
resistance to a shearing stress.
The
viscosity of a liquid decreases with the increase of temperature due to
decrease of molecular cohesion between molecules and this is responsible for reduction
in liquid viscosity. But is case of gas viscosity increases with the increase
of temperature due to greater molecular activity as the temperature increases.
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