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Chapter 13
Fluids
© 2010 Pearson Education, Inc.
PowerPoint® Lectures for
College Physics: A Strategic Approach, Second Edition
13 Fluids
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Slide 13-2
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Slide 13-3
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Slide 13-4
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Reading Quiz
1. The SI unit of pressure is
A.
B.
C.
D.
N
kg/m2
Pa
kg/m3
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Slide 13-6
Answer
1. The SI unit of pressure is
A.
B.
C.
D.
N
kg/m2
Pa
kg/m3
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Reading Quiz
2. Gauge pressure is
A.
B.
C.
D.
true pressure. Explain.
larger than
smaller than
the same as
None of the above
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Slide 13-8
Answer
2. Gauge pressure is
A.
B.
C.
D.
true pressure. Explain.
larger than
smaller than
the same as
None of the above
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Slide 13-9
Reading Quiz
3. The buoyant force on an object submerged in a liquid depends
on
A.
B.
C.
D.
the object’s mass.
the object’s volume.
the density of the liquid.
both B and C.
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Slide 13-10
Answer
3. The buoyant force on an object submerged in a liquid depends
on
A.
B.
C.
D.
the object’s mass.
the object’s volume.
the density of the liquid.
both B and C.
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Density
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Slide 13-12
Pressure
F
p=
A
The pressure of the
water behind each hole
pushes the water out.
The SI unit of pressure is 1 pascal = 1 Pa = 1 N/m2.
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Slide 13-13
Pressure in a Liquid Increases with Depth
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Example Problem
In a graduated cylinder, 10 cm of oil (ρ = 0.85 g/cm3) floats on
top of 20 cm of water (ρ = 1.00 g/cm3). What is the pressure at
a height of 10 cm from the bottom of the cylinder?
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Atmospheric Pressure
patmos = 1 atm = 103,000 Pa
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Example Problem
The gas in the cylinder is at a pressure of
pgas = 3.0 x 105 Pa. How high is the column of mercury?
3
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The Barometer
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Pressure Units
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Buoyancy
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FB = rfVf g
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Floating
When the object sinks to the point
that the weight of the displaced fluid
equals the weight of the object, then
the forces balance and the object
floats in equilibrium. No net force.
The volume of fluid displaced by a
floating object of density o and
volume Vo is
po
Vf = Vo
pf
The density of ice is 90% that of water.
When ice floats, the displaced water is
90% of the volume of ice. Thus 90% of
the ice is below water and 10% is above.
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How a Boat Floats
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Slide 13-24
Checking Understanding
Two blocks of identical size are submerged in water. One is made
of lead (heavy), the other of aluminum (light). Upon which is the
buoyant force greater?
A. On the lead block.
B. On the aluminum block.
C. They both experience the same buoyant force.
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Slide 13-25
Answer
Two blocks of identical size are submerged in water. One is made
of lead (heavy), the other of aluminum (light). Upon which is the
buoyant force greater?
A. On the lead block.
B. On the aluminum block.
C. They both experience the same buoyant force.
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Slide 13-26
Checking Understanding
Two blocks are of identical size. One is made of lead, and sits on
the bottom of a pond; the other is of wood and floats on top. Upon
which is the buoyant force greater?
A. On the lead block.
B. On the wood block.
C. They both experience the same buoyant force.
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Slide 13-27
Answer
Two blocks are of identical size. One is made of lead, and sits on
the bottom of a pond; the other is of wood and floats on top. Upon
which is the buoyant force greater?
A. On the lead block.
B. On the wood block.
C. They both experience the same buoyant force.
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Slide 13-28
Checking Understanding
A barge filled with ore floats in a canal lock. If the ore is tossed
overboard into the lock, the water level in the lock will
A. rise.
B. fall.
C. remain the same.
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Answer
A barge filled with ore floats in a canal lock. If the ore is tossed
overboard into the lock, the water level in the lock will
A. rise.
B. fall.
C. remain the same.
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Slide 13-30
Example Problem
A block of plastic floats in water. 20% of the block’s volume
is above the waterline. What is the density of the block?
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Example Problem
A ball weighing 1.0 N has a density 1/3 that of water. What
is the tension in the string when the ball is held under water
as shown?
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Constrained Flow: Continuity
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Acceleration of Fluids
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Pressure Gradient in a Fluid
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Bernoulli’s Equation
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Example Problem
In an agricultural irrigation system, water is pumped through a
constant-diameter pipe up a 1.5-m-high embankment, where it
empties into a field. If the farmer wants to pump water at a rate of
20 L/s, what pressure does his pump need to apply at the bottom
of the pipe?
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Viscosity
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Poiseuille’s Equation
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Example Problem
A garden hose is 10 m long and has an inner diameter of 2.5
cm. Using this hose it takes 5.0 s to fill a 10 L bucket. What is
the water pressure at the spigot end of the hose?
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Summary
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Summary
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