Chapter Menu

1
Chapter Menu
Chapter Introduction Lesson 1 Pressure and
Density of Fluids Lesson 2 The Buoyant
Force Lesson 3 Other Effects of Fluid
Forces Chapter Wrap-Up
2
Chapter Introduction

• In what ways do people use forces in fluids?

3
Chapter Introduction

• What do you think?

Before you begin, decide if you agree or disagree
with each of these statements. As you view this
presentation, see if you change your mind about
any of the statements.
4
Chapter Introduction
Do you agree or disagree?

• 1. Air is fluid.
• 2. Pressure is a force acting on a fluid.
• 3. You can lift a rock easily under water because
  there is a buoyant force on the rock.

5
Chapter Introduction
Do you agree or disagree?

• 4. The buoyant force on an object depends on the
  objects weight.
• 5. If you squeeze an unopened plastic ketchup
  bottle, the pressure on the ketchup changes
  everywhere in the bottle.
• 6. Running with an open parachute decreases the
  drag force on you.

6
Lesson 1 Reading Guide - KC
Pressure and Density of Fluids

• How do force and area affect pressure?
• How does pressure change with depth in the
  atmosphere and under water?
• What factors affect the density of a fluid?

7
Lesson 1 Reading Guide - Vocab
Pressure and Density of Fluids

• fluid
• pressure
• atmospheric pressure

8
Lesson 1-1
What is a fluid?

• A fluid is any substance that can flow and take
  the shape of the container that holds it.

fluid from Latin fluidus, means flowing
9
Lesson 1-1
What is a fluid? (cont.)

• The volume of a liquid is constant, regardless of
  the container.
• The volume of a gas always changes to fill the
  container.

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10
Lesson 1-2
Pressure of Fluids

• Pressure is the amount of force per unit area
  applied to an objects surface.
• All fluids (liquids and gases) apply pressure.
• Pressure applied on an object by a fluid is
  related to the weight of the fluid.

11
Lesson 1-2
Pressure of Fluids (cont.)

• In the equation below, P is pressure, f is the
  force applied to a surface, and a is the surface
  area over which the force is applied.
• The unit measurement for pressure is the pascal
  (Pa).

12
Lesson 1-2
Pressure of Fluids (cont.)
13
Lesson 1-2
Pressure of Fluids (cont.)

• A fluid applies pressure perpendicular to all
  sides of an object in contact with the fluid.

14
Lesson 1-2
Pressure of Fluids (cont.)

• Pressure decreases when the surface area over
  which a force is applied increases.
• Pressure increases when the surface area over
  which a force is applied decreases.

15
Lesson 1-2
Pressure of Fluids (cont.)
How does pressure change as surface area changes?
16
Lesson 1-2
Pressure of Fluids (cont.)

• The ratio of the weight of all the air above you
  to your surface area is atmospheric pressure.

17
Lesson 1-2

• On land, atmospheric pressure depends on your
  elevation.

18
Lesson 1-2

• Under water, the pressure depends on your depth
  below the waters surface.

19
Lesson 1-2
Pressure of Fluids (cont.)
How does elevation affect atmospheric pressure?
20
Lesson 1-3
Density of Fluids

• If the volume of two fluids is the same, the
  fluid that weighs more is denser.

dense Science Use a measure of the ratio of mass
to volume Common Use slow to learn or understand
21
Lesson 1-3
Density of Fluids (cont.)

• You can calculate density with the equation
  below, where D is density, m is mass, and v is
  volume.
• Density is often measured in grams per cubic
  centimeter (g/cm3).

22
Lesson 1-3
Density of Fluids (cont.)

• Materials have different densities because of
  differences in the masses of their molecules and
  in the distances between them.
• Solids are usually denser than liquids or gases.

23
Lesson 1-3
Density of Fluids (cont.)
What factors determine the density of fluids?
24
Lesson 1 - VS

• Pressure is high when a force is applied over a
  small area.

25
Lesson 1 - VS

• Atmospheric pressure decreases with elevation.

26
Lesson 1 - VS

• Fluids form layers depending on their densities.

27
Lesson 1 LR1
Which term refers to the ratio of the weight of
all the air above you to your surface area?
A. atmospheric pressure B. density C. elevation
D. pascal
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Lesson 1 LR2
What happens to pressure applied by a fluid as
depth increases?
A. decreases B. increases C. fluctuates
randomly D. remains the same
29
Lesson 1 LR3
By what do you divide mass to calculate density?
A. volume B. pressure C. force D. area
30
Lesson 1 - Now
Do you agree or disagree?

• 1. Air is fluid.
• 2. Pressure is a force acting on a fluid.

31
Lesson 2 Reading Guide - KC
The Buoyant Force

• How are pressure and the buoyant force related?
• How does Archimedes principle describe the
  buoyant force?
• What makes an object sink or float in a fluid?

32
Lesson 2 Reading Guide - Vocab
The Buoyant Force

• buoyant force
• Archimedes principle

33
Lesson 2-1
What is a buoyant force?

• A buoyant force is an upward force applied by a
  fluid on an object in the fluid.

buoyant from Spanish boyar, means to float
34
Lesson 2-1
What is a buoyant force? (cont.)

• A buoyant force acts on any object in a liquid.
  Objects in a gas also experience a buoyant force.

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Getty Images/Digital Vision
35
Lesson 2-1

• The buoyant force on a diver is the difference
  between the force from pressure above and below
  the diver.

36
Lesson 2-1
What is a buoyant force? (cont.)
How is pressure related to buoyant force?
37
Lesson 2-1
What is a buoyant force? (cont.)

• The depth of an object completely submerged in a
  fluid has no effect on the buoyant force.
• The buoyant force depends on an objects volume.

38
Lesson 2-2
Archimedes Principle

• The greater the volume of an object in a fluid,
  the greater the buoyant force on it.
• Archimedes principle states that the buoyant
  force on an object is equal to the weight of the
  fluid that the object displaces.

39
Lesson 2-2

• The buoyant force is greater on the balloon than
  on the tennis ball or the billiard ball because
  the balloon displaces more water.

40
Lesson 2-2
Archimedes Principle (cont.)
What is the buoyant force on you if you displace
400 N of water as you dive under water?
41
Lesson 2-2
Sinking and Floating

• When the buoyant force on an object is less than
  the gravitational force, the object sinks.
• An object floats if the buoyant force acting on
  it is equal to the objects weight.

42
Lesson 2-2

• If the weight of an object is greater than the
  buoyant force acting on it, the object sinks.

43
Lesson 2-2
Sinking and Floating (cont.)

• If an object is more dense than the fluid in
  which it is placed, then the buoyant force on
  that object will be less than the objects
  weight, and the object will sink.

If an object weighing 14 N experiences a 12-N
buoyant force, will it sink or float?
44
Lesson 2-2

• The boat on the left floats because it is filled
  with air instead of water.

45
Lesson 2-2

• As a balloon loses helium, its density increases
  and its buoyant force decreases.

46
Lesson 2 - VS

• A buoyant force results from the difference in
  pressure between the top and the bottom of an
  object?

47
Lesson 2 - VS

• Objects that have the same volume in a fluid
  experience the same buoyant force.

48
Lesson 2 - VS

• When the density of a balloon becomes greater
  than the density of air, the balloon sinks.

49
Lesson 2 LR1
What is the direction of a buoyant force?
A. upward B. horizontal C. downward D. diagonal
50
Lesson 2 LR2
How does increasing the depth of an object in a
fluid affect the buoyant force on the fluid?
A. It has no effect. B. It decreases the buoyant
force. C. It increases the buoyant force. D. The
effect depends on the objects depth.
51
Lesson 2 LR3
An object floats if the buoyant force is which of
these?
A. equal to the objects weight B. greater than
the objects weight C. less than atmospheric
pressure D. less than the objects weight
52
Lesson 2 - Now
Do you agree or disagree?
3. The buoyant force on an object depends on the
objects weight. 4. You can lift a rock easily
under water because there is a buoyant force on
the rock.
53
Lesson 3 Reading Guide - KC
Other Forces in Fluids

• How are forces transferred through a fluid?
• How does Bernoullis principle describe the
  relationship between pressure and speed?
• What affects drag forces?

54
Lesson 3 Reading Guide - Vocab
Other Forces in Fluids

• Pascals principle
• Bernoullis principle
• drag force

55
Lesson 3-1
Fluid ForcesBenefits and Challenges

• You produce a force when you squeeze a plastic
  ketchup bottle.
• You make use of a buoyant force when you float on
  a raft.
• Fluid forces from floods, tornadoes, and
  hurricanes can cause damage.

56
Lesson 3-2
Pascals Principle

• Pascals principle states that when pressure is
  applied to a fluid in a closed container, the
  pressure increases by the same amount everywhere
  in the container.

57
Lesson 3-2
Pascals Principle (cont.)
How does pressure change when force is applied to
a fluid in a closed container?
58
Lesson 3-2
Pascals Principle (cont.)

• A piston uses a small force in one area to apply
  a larger force in another area.
• According to Pascals principle, pushing on the
  piston increases the pressure equally throughout
  the fluid in the piston.

59
Lesson 3-2

• Car mechanics rely on Pascals principle when
  they raise a car using a hydraulic lift.
• Pushing down with a small force in the narrow
  tube generates a force under the car that is
  large enough to lift the car.

60
Lesson 3-2

• The piston on the left will have to be pushed
  down further than the distance the car will be
  raised.
• Since work is force times distance, the work
  done by the two pistons is equal.

61
Lesson 3-3
Bernoullis Principle

• Bernoullis principle states that the pressure of
  a fluid decreases when the speed of that fluid
  increases.

62
Lesson 3-3
Bernoullis Principle (cont.)
What is the relationship between speed and
pressure in a fluid?
63
Lesson 3-3
Bernoullis Principle (cont.)
64
Lesson 3-3
Bernoullis Principle (cont.)
How does Bernoullis principle explain how wind
can take the roof off a house?
65
Lesson 3-3

• Because air moves from areas of high to low
  pressure, the higher pressure on the left side of
  the soccer ball causes the ball to curve right.

66
Lesson 3-4
Drag Forces

• Drag force is a force that opposes the motion of
  an object through a fluid.

drag force from Old Norse draga, means to
draw and Latin fortis, means force
67
Lesson 3-4
Drag Forces (cont.)

• As the speed of an object in a fluid increases,
  the drag force on that object also increases.
• If two objects move in the same direction, the
  object with the greater surface area toward the
  direction of the motion has a greater drag force
  on it.
• Drag forces increase when the density of a fluid
  increases.

68
Lesson 3-4
Drag Forces (cont.)
What affects the drag force on an object?
69
Lesson 3 - VS

• People rely on Pascals principle when they use
  hydraulic lifts.
• The imbalance of pressures in fluids can cause
  a roof to lift off a house in a severe
  windstorm.

70
Lesson 3 - VS

• A soccer player who kicks a curved ball makes use
  of Bernoullis principle.

71
Lesson 3 LR1
Which states that pressure in a closed container
is applied equally?
A. Archimedes principle B. Bernoullis
principle C. drag force principle D. Pascals
principle
72
Lesson 3 LR2
What is the relationship between the amount of
work on the two pistons of a closed fluid system?
A. More work is done on the larger side. B. More
work is done on the smaller side. C. No work is
done on either side. D. The amount of work is
the same on both sides.
73
Lesson 3 LR3
Which states that the pressure of a fluid
decreases when the speed of that fluid increases?
A. Archimedes principle B. Bernoullis
principle C. drag force principle D. Pascals
principle
74
Lesson 3 - Now
Do you agree or disagree?
5. If you squeeze an unopened plastic ketchup
bottle, the pressure on the ketchup changes
everywhere in the bottle. 6. Running with an open
parachute decreases the drag force on you.
75
Chapter Review Menu
Key Concept Summary Interactive Concept
Map Chapter Review Standardized Test Practice
76
The BIG Idea

• People use forces in fluids to float objects on
  water and in air, to lift objects, and to affect
  the motions of objects.

77
Key Concepts 1
Lesson 1 Pressure and Density of Fluids

• Pressure is the ratio of force to area.
• Atmospheric pressure decreases with elevation.
  Pressure under water increases with depth.
• The density of a fluid depends on the mass of
  the fluid and its volume.

78
Key Concepts 2
Lesson 2 The Buoyant Force

• The change in pressure between the top and the
  bottom of an object results in an upward force
  called the buoyant force.
• Archimedes principle states that the weight of
  the fluid displaced by an object is equal to the
  buoyant force on that object.
• An object sinks if its weight is greater than
  the buoyant force on it. An object does not sink
  if the buoyant force on it is equal to its weight.

79
Key Concepts 3
Lesson 3 Other Forces from Fluids

• Pascals principle states that when pressure is
  applied to a fluid in a closed container, the
  pressure increases by the same amount everywhere
  in the container.
• Bernoullis principle states that when the speed
  in a fluid increases, the pressure decreases.
• Speed, size, and shape of an object, as well as
  the density of the fluid in which the object
  moves, affect the drag force on that object.

80
Chapter Review MC1
Which term describes the amount of force per unit
area applied to an objects surface?
A. atmospheric pressure B. drag force C. fluid
D. pressure
81
Chapter Review MC2
By what do you divide force to calculate pressure?
A. area B. mass C. volume D. weight
82
Chapter Review MC3
Which describes an upward force applied by a
fluid on an object in the fluid?
A. pressure B. gravity C. density D. buoyant
force
83
Chapter Review MC4
The buoyant force on a diver is the difference
between the upward force from pressure and which
of these?
A. the depth of the water B. the downward force
from pressure C. the density of the diver D. the
density of the fluid
84
Chapter Review MC5
What happens to the atmospheric pressure as you
hike a trail to the top of a mountain?
A. it decreases B. it increases C. it first
decreases, then increases D. if first increases,
then decreases
85
Chapter Review STP1
Which term describes any substance that can flow
and take the shape of the container that holds it?
A. fluid B. gas C. liquid D. solid
86
Chapter Review STP2
Which is the unit measurement for pressure?
A. grams per cubic centimeter B. joule C. pascal D
. newton
87
Chapter Review STP3
Archimedes principle states that the buoyant
force on an object is equal to what?
A. the depth of the object B. the surface area of
the object C. the weight of the displaced fluid
D. the weight of the object
88
Chapter Review STP4
Which describes a force that opposes the motion
of an object through a fluid?
A. atmospheric pressure B. buoyant force C. drag
force D. friction
89
Chapter Review STP5
What happens to the drag force on an object in a
fluid as the speed of the object increases?
A. It decreases. B. It depends on the shape of
the object. C. It increases. D. It remains
constant.