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Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
PowerPoint® Lectures for
University Physics, Twelfth Edition
– Hugh D. Young and Roger A. Freedman
Lectures by James Pazun
Chapter 14
Fluid Mechanics
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Buoyancy and Archimedes Principle
• The buoyant force is equal to the weight of the displaced fluid.
• Refer to Figure 14.12.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Buoyancy and Archimedes Principle II
• Consider
Example 14.5.
• Refer to Figure
14.14 as you
read Example
14.5.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
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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