This document discusses key concepts in fluid mechanics including: - Fluid mechanics is divided into static, kinematic, and dynamic branches which study fluids at rest, geometry of motion, and relationship between motion and forces. - Density, specific weight, specific volume, viscosity, and kinematic viscosity are important fluid properties defined and their units discussed. - Viscosity describes a fluid's resistance to layers moving relative to each other, proportional to velocity gradient. Kinematic viscosity is the ratio of dynamic viscosity to density.

1. •Introduction
•Nomenclature
•Dimensions and Units
•Density or Mass Density
•Specific Weight or Weight Density
•Specific Volume
•Viscosity
•Kinematic Viscosity

2.  Fluid Mechanics is the study of behaviour of gases
and liquids. The study of fluids in motion is called
Fluid Dynamics. The study of fluids at rest is called
Fluid Statics.
 Applications of fluid mechanics are found in a
variety of engineering disciplines such as
aerospace, biomedical, civil, mechanical etc.
 A wide variety of fluid mechanics applications are
apparent across many disciplines, however
fundamentals of fluid mechanics that form the
bases of these applications are relatively few.

3.  Fluid mechanics can be divided into three
branches: static, kinematics and dynamics.
 Fluid Statics is the study of the mechanics of
fluids at rest, kinematics is the study of
geometry of fluid motions and dynamics is the
study of the relationship between fluid motion
and the forces action on fluids.
 Fluid Dynamics is further divided into several
specific areas. The study of fluid dynamics
when the fluid is incompressible and
frictionless is called hydro-dynamics.

4.  In fluid mechanic applications, the SI
fundamental dimensions that are generally used
include mass[M], length[L], time[t],
temperature[T], and amount of substance[mol].
In USCS system, force[F] replaces mass[M] as a
fundamental dimension.
 Fundamental dimensions are sometimes
referred to as primary dimensions, with
dimensions derived from combinations of
primary dimensions being referred to as
secondary dimensions.

5.  Density or mass density of a fluid is defined as ratio of
the mass of fluid to its volume. Thus mass per unit
volume of a fluid is called density. The unit of mass
density in SI unit kg per cubic metric i.e., kg/m^3.
 Mathematically, mass density is written as
 The value of density of water is 1gm/cm^3 or
1000kg/m^3.

6. Specific weight of a fluid is the ratio
between the weight of a fluid to its volume.
Thus weight per unit volume of a fluid is
called weight density and it is denoted by
the symbol w.
The value of specific weight of water is
9.81 x 1000 Newton/m^3 in SI units.

7. Specific volume of a fluid is defined as the
ratio of weight density of liquid/gas to the
weight density of water/air of liquid.

8.  Viscosity is defined as the property of a fluid which offers resistance to the movement
of one layer of fluid over another adjacent layer of the fluid. When two layers of a fluid,
a distance ‘dy’ apart, move with relative velocity causes a shear stress acting between
the fluid layers.
 The top layer causes a shear stress on the adjacent lower layer while the lower layer
causes a shear stress on the adjacent top layer. This shear stress is proportional to
the rate of change of velocity with respect to ‘y’. It is denoted by symbol τ (Tau).
 Where, μ (called Mu) is the constant of proportionality and is known as co-efficient of
dynamic viscosity or only viscosity. (du/dy) represents the rate of shear strain or rate
of shear deformation or velocity gradient.
 The viscosity is also defined as the shear stress required to produce unit rate of shear
strain.
 SI unit of viscosity = N*s/m^2=Pa s.

9. It is defined as the ratio between the
dynamic viscosity and density of fluid. It is
denoted by the Greek symbol (v) called
‘nu’.
SI unit of kinematic viscosity is
meter^2/sec. In CGS units kinematic
viscosity is also known as stoke.