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![Page 1: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/1.jpg)
Preview
• Objectives
• Defining a Fluid
• Density and Buoyant Force
• Sample Problem
Chapter 8Section 1 Fluids and Buoyant Force
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Section 1 Fluids and Buoyant ForceChapter 8
Objectives
• Define a fluid.
• Distinguish a gas from a liquid.
• Determine the magnitude of the buoyant force exerted on a floating object or a submerged object.
• Explain why some objects float and some objects sink.
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Section 1 Fluids and Buoyant ForceChapter 8
Defining a Fluid
• A fluid is a nonsolid state of matter in which the atoms or molecules are free to move past each other, as in a gas or a liquid.
• Both liquids and gases are considered fluids because they can flow and change shape.
• Liquids have a definite volume; gases do not.
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Section 1 Fluids and Buoyant ForceChapter 8
Density and Buoyant Force
• The concentration of matter of an object is called the mass density.
• Mass density is measured as the mass per unit volume of a substance.
m
V
mass density mass
volume
![Page 5: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/5.jpg)
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Visual Concept
Chapter 8Section 1 Fluids and Buoyant Force
Mass Density
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Section 1 Fluids and Buoyant ForceChapter 8
Density and Buoyant Force, continued
• The buoyant force is the upward force exerted by a liquid on an object immersed in or floating on the liquid.
• Buoyant forces can keep objects afloat.
![Page 7: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/7.jpg)
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Chapter 8Section 1 Fluids and Buoyant Force
Buoyant Force and Archimedes’ Principle
Visual Concept
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Chapter 8
Displaced Volume of a Fluid
Section 1 Fluids and Buoyant Force
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Section 1 Fluids and Buoyant ForceChapter 8
Density and Buoyant Force, continued
• Archimedes’ principle describes the magnitude of a buoyant force.
• Archimedes’ principle: Any object completely or partially submerged in a fluid experiences an upward buoyant force equal in magnitude to the weight of the fluid displaced by the object.
FB = Fg (displaced fluid) = mfg
magnitude of buoyant force = weight of fluid displaced
![Page 10: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/10.jpg)
Click below to watch the Visual Concept.
Visual Concept
Chapter 8Section 1 Fluids and Buoyant Force
Buoyant Force on Floating Objects
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Chapter 8
Buoyant Force
Section 1 Fluids and Buoyant Force
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Section 1 Fluids and Buoyant ForceChapter 8
Density and Buoyant Force, continued
• For a floating object, the buoyant force equals the object’s weight.
• The apparent weight of a submerged object depends on the density of the object.
• For an object with density O submerged in a fluid of density f, the buoyant force FB obeys the following ratio:
Fg(object)
FB
O
f
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem
Buoyant Force
A bargain hunter purchases a “gold” crown at a flea market. After she gets home, she hangs the crown from a scale and finds its weight to be 7.84 N. She then weighs the crown while it is immersed in water, and the scale reads 6.86 N. Is the crown made of pure gold? Explain.
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem, continued
Buoyant Force1. DefineGiven:
Fg = 7.84 Napparent weight = 6.86 N
f = pwater = 1.00 103 kg/m3
Unknown:
O = ?
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Section 1 Fluids and Buoyant ForceChapter 8
Diagram:
Sample Problem, continued
Buoyant Force1. Define, continued
TIP: The use of a diagram can help clarify a problem and the variables involved. In this diagram, FT,1 equals the actual weight of the crown, and FT,2 is the apparent weight of the crown when immersed in water.
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem, continued
Buoyant Force2. Plan
Choose an equation or situation: Because the object is completely submerged, consider the ratio of the weight to the buoyant force.
– apparent weightg B
g O
B f
F F
F
F
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem, continued
Buoyant Force2. Plan, continued
Rearrange the equation to isolate the unknown:
– apparent weightB g
gO f
B
F F
F
F
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem, continued
Buoyant Force3. Calculate
Substitute the values into the equation and solve:
3 3
3 3
7.84 N – 6.86 N = 0.98 N
7.84 N1.00 10 kg/m
0.98 N
8.0 10 kg/m
B
gO f
B
O
F
F
F
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Section 1 Fluids and Buoyant ForceChapter 8
Sample Problem, continued
Buoyant Force4. Evaluate
From the table, the density of gold is 19.3 103 kg/m3. Because 8.0 103 kg/m3 < 19.3 103 kg/m3, the crown cannot be pure gold.
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Preview
• Objectives
• Pressure
Chapter 8 Section 2 Fluid Pressure
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Section 2 Fluid PressureChapter 8
Objectives
• Calculate the pressure exerted by a fluid.
• Calculate how pressure varies with depth in a fluid.
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Section 2 Fluid PressureChapter 8
Pressure
• Pressure is the magnitude of the force on a surface per unit area.
• Pascal’s principle states that pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container.
P F
A
pressure = force
area
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Click below to watch the Visual Concept.
Visual Concept
Chapter 8 Section 2 Fluid Pressure
Pascal’s Principle
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Section 2 Fluid PressureChapter 8
Pressure, continued
• Pressure varies with depth in a fluid.
• The pressure in a fluid increases with depth.
0
absolute pressure =
atmospheric pressure +
density free-fall acceleration depth
P P gh
![Page 25: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/25.jpg)
Click below to watch the Visual Concept.
Visual Concept
Chapter 8 Section 2 Fluid Pressure
Fluid Pressure as a Function of Depth
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Preview
• Objectives
• Fluid Flow
• Principles of Fluid Flow
Chapter 8 Section 3 Fluids in Motion
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Section 3 Fluids in MotionChapter 8
Objectives
• Examine the motion of a fluid using the continuity equation.
• Recognize the effects of Bernoulli’s principle on fluid motion.
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Section 3 Fluids in MotionChapter 8
Fluid Flow
• Moving fluids can exhibit laminar (smooth) flow or turbulent (irregular) flow.
• An ideal fluid is a fluid that has no internal friction or viscosity and is incompressible.
• The ideal fluid model simplifies fluid-flow analysis.
![Page 29: Preview Objectives Defining a Fluid Density and Buoyant Force Sample Problem Chapter 8 Section 1 Fluids and Buoyant Force.](https://reader035.fdocuments.net/reader035/viewer/2022062321/56649f205503460f94c38a82/html5/thumbnails/29.jpg)
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Visual Concept
Chapter 8 Section 3 Fluids in Motion
Characteristics of an Ideal Fluid
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Section 3 Fluids in MotionChapter 8
Principles of Fluid Flow
• The continuity equation results from conserva-tion of mass.
• Continuity equation
A1v1 = A2v2
Area speed in region 1 = area speed in region 2
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Section 3 Fluids in MotionChapter 8
Principles of Fluid Flow, continued
• The speed of fluid flow depends on cross-sectional area.
• Bernoulli’s principle states that the pressure in a fluid decreases as the fluid’s velocity increases.
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Visual Concept
Chapter 8 Section 3 Fluids in Motion
Bernoulli’s Principle