General Physics
Hawassa, Ethiopia
BY:
Mideksa
K.(MSc.)
August,2021
Chapter Three
Fluid
PROPERTIES OF BULK MATTER
Elastic Behavior
Elastic Material
Elastic Deformation Plastic Materials
Stress/stra
Mechanical
in
Energy
Tensile
Shear
Volume
Elasticity Moduli
Young’s Modulus
The ratio of the tensile stress to the tensile strain.
Shear Modulus
(S)
The ratio of shear stress to shear strain.
Bulk Modulus
Example
The ratio of Volume stress to Volume strain.
A2.0-m-long,1.0-mm-diameter wire is suspended from
the ceiling. Hanging a 4.5 kg mass from the wire
stretches the wire’s length by 1.0 mm. What is Young’s
modulus for this wire? Can you identify the material?
Example 2. The area of cross section of a steel wire (Y = 2.0x1011 N/m2) is 0.1 cm2. Calculate the force required to double its length.
Example
A load of 2.0 kg is applied to the ends of a wire 4.0 m long, and produces an extension of
0.24 mm. If the diameter of the wire is 2.0 mm, find: the stress on the wire and the strain it
produces.
Density and Pressure
Density
Specific Gravity
The quantity of mass (m) per unit volume (V) of a body.
The ratio of the density of the substance to the
density of another substance which is taken as a
standard
Pressure
A normal compressive force exerted by a fluid per unit area.
Atmospheric Pressure
Gauge Pressure
The weight the air exerts on
you
Example
The surface of the water in a storage tank is 30 m above a water faucet
in the kitchen of a house, Calculate the difference in water pressure
between the faucet and the surface of the water in the tank.
Absolute Pressure
The pressure
measured from zero (0)
value
Buoyant Force
Pascal’s Principle
The pressure of a gas or liquid exerts
force equally in all directions against the
walls of its container.
Example
The hydraulic lift at a car repair shop is filled with oil. The car
rests on a 25-cm-diameter piston. To lift the car, compressed
air is used to push down on a 6.0-cm-diameter piston. What
does the pressure gauge read when a 1300 kg car is 2.0 m
above the compressed-air piston?
The buoyancy force is equal to
Archimedes’ Principle
the weight of the fluid displaced.
Example
A 10 cm x 10 cm x 10 cm block of wood with
density 700 kg/m3 is held underwater by a string
tied to the bottom of the container. What is the
tension in the string?
Fluid Dynamics
Laminar
When the particles of fluid move along straight line path or
parallel to each other
Factors
affecting
laminar
flow
are
density,
compressibility, temperature and viscosity of the fluid.
Turbulence
Irregular flow characterized by small whirlpool-like regions,
Equation of continuity
The volume flow rate is constant at all points in a tube.
Bernoulli’s Equation
For an incompressible , inviscid flow and steady
flow, energy per unit volume is constant throughout
the flow.”
Example
Water flows through the pipes shown in Figure .The
water’s speed through the lower pipe is 5.0 m/s and a
pressure gauge reads 75 kPa. What is the reading of the
pressure gauge on the upper pipe?
Application of Bernoulli’s Equation
Torricelli theorem
Airplane Wings and Dynamic Lift