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PowerPoint
®
Lectures for
University Physics, Twelfth Edition
–
Hugh D. Young and Roger A. Freedman
Lectures by James Pazun
Chapter 14
Fluid Mechanics
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Goals for Chapter 14
•
To study density and pressure
•
To consider pressures in a fluid at rest
•
To shout “Eureka” with Archimedes and overview
buoyancy
•
To turn our attention to fluids in motion and calculate
the effects of changing openings, height, density,
pressure, and velocity
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Introduction
•
Submerging bath toys and
watching them pop back up
to the surface is an
experience with Archimedes
Principle.
•
Fish move through water
with little effort and their
motion is smooth. Consider
the shark at right … it must
keep moving for its gills to
operate properly.
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Density does not depend on the size of the object
•
Density is a measure of
how much mass occupies
a given volume.
•
Refer to Example 14.1
and Table 14.1 (on the
next slide) to assist you.
•
Density values are
sometimes divided by the
density of water to be
tabulated as the unit less
quantity, specific gravity.
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Densities of common substances
—
Table 14.1
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The pressure in a fluid
•
Pressure in a fluid is
force per unit area. The
Pascal is the given SI unit
for pressure.
•
Refer to Figures 14.3 and
14.4.
•
Consider Example 14.2.
•
Values to remember for
atmospheric pressure
appear near the bottom of
page 458.
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Pressure, depth, and Pascal’s Law
•
Pressure is everywhere equal in a uniform fluid of equal depth.
•
Consider Figure 14.7 and a practical application in Figure 14.8.
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Finding absolute and gauge pressure
•
Pressure from the fluid and pressure from the air above it
are determined separately and may or may not be combined.
•
Refer to Example 14.3 and Figure 14.9.
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There are many clever ways to measure pressure
•
Refer to Figure 14.10.
•
Follow Example 14.4.
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Measuring the density of a liquid
•
Have you ever
seen the
barometers made
from glass spheres
filled with various
densities of liquid?
This is their
driving science.
•
Refer to Figure
14.13.
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Buoyancy and Archimedes Principle
•
The buoyant force is equal to the weight of the displaced fluid.
•
Refer to Figure 14.12.
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Buoyancy and Archimedes Principle II
•
Consider
Example 14.5.
•
Refer to Figure
14.14 as you
read Example
14.5.
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Surface tension
•
How is it that
water striders can
walk on water
(although they are
more dense than
the water)?
•
Refer to Figure
14.15 for the
water strider and
then Figures 14.16
and 14.17 to see
what’s occurring
from a molecular
perspective.
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Fluid flow I
•
The flow lines at left in Figure 14.20 are laminar.
•
The flow at the top of Figure 14.21 is turbulent.
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Fluid flow II
•
The
incompressibility
of fluids allows
calculations to be
made even as pipes
change.
•
Refer to Figure
14.22 as you
consider Example
14.6.
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Bernoulli’s equation
•
Bernoulli’s equation allows
the user to consider all
variables that might be
changing in an ideal fluid.
•
Refer to Figure 14.23.
•
Consider Problem

Solving
Strategy 14.1.
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Water pressure in a home (Bernoulli’s Principle II)
•
Consider
Example 14.7.
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Speed of efflux (Bernoulli’s Equation III)
•
Refer to
Example 14.8.
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The Venturi meter (Bernoulli’s Equation IV)
•
Consider Example 14.9.
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Lift on an airplane wing
•
The first time I saw lift
from a flowing fluid, a man
was holding a Ping

Pong
ball in a funnel while
blowing out. A wonderful
demonstration to go with
the lift is by blowing across
the top of a sheet of paper.
•
Refer to Conceptual
Example 14.10.
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Viscosity and turbulence
—
Figures 14.28, 14.29
•
When we cease to treat
fluids as ideal, molecules
can attract or repel one
another
—
they can interact
with container walls and
the result is turbulence.
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A curve ball (Bernoulli’s equation applied to sports)
•
Bernoulli’s equation allows us to explain why a curve ball
would curve, and why a slider turns downward.
•
Consider Figure 14.31.
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