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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


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


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.


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.


Densities of common substances—Table 14.1


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.


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.


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.


There are many clever ways to measure pressure

• Refer to Figure 14.10.

• Follow Example 14.4.


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.


Buoyancy and Archimedes Principle

• The buoyant force is equal to the weight of the displaced fluid.



Buoyancy and Archimedes Principle II

• Consider

Example 14.5.

• Refer to Figure

14.14 as you

read Example

14.5.


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.


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.


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.


Bernoulli’s equation

• Bernoulli’s equation allows

the user to consider all

variables that might be

changing in an ideal fluid.


• Consider Problem-Solving

Strategy 14.1.


Water pressure in a home (Bernoulli’s Principle II)

• Consider

Example 14.7.


Speed of efflux (Bernoulli’s Equation III)

• Refer to

Example 14.8.


The Venturi meter (Bernoulli’s Equation IV)

• Consider Example 14.9.


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.


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.


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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