Properties of Matter

1. Unit 8, Chapter27
CPO Science
Foundations of Physics

2. Unit 8: Matterand Energy
 27.1 Properties of Solids
 27.2 Properties of Liquids and Fluids
 27.3 Properties of Gases
Chapter27 The Physical Properties of Matter

3. Chapter27 Objectives
1. Performcalculations involving the density of solids, gases, and
liquids.
2. Apply the concepts of force, stress, strain, and tensile strength to
simple structures.
3. Describe the cause and some consequences of thermal expansion in
solids, liquids, and gases.
4. Explain the concept of pressure and calculate pressure caused by
the weight of fluids.
5. Explain how pressure is created on a molecularlevel.
6. Understand and apply Bernoulli’s equation to flow along a
streamline.
7. Apply the gas laws to simple problems involving pressure,
temperature, mass, and volume.

4. Chapter27 Vocabulary Terms
 stress
 density
 strain
 tensile strength
 cross section area
 pressure
 volume
 tension
 compression
 elastic, elasticity
 fluid
 brittle
 ductile
 safety factor
 modulus of
elasticity
 alloy
 airfoil
 buoyancy
 fluid mechanics
 ideal gas law
 Boyle’s law
 streamline
 laminarflow
 turbulent flow
 Bernoulli’s
equation
 pascal (Pa)
 Charles’ law
 gas constant (R)
 composite
material
 thermal expansion

5. 27.1 Properties of Solids
Key Question:
How do you measure the
strength of a solid
material?
*Students read Section 27.1
AFTER Investigation 27.1

6. 27.1 Properties of Solids
 The density of a
material is the ratio of
mass to volume.
 Density is a physical
property of the material
and stays the same no
matter how much
material you have.

7. 27.1 Density
ρ = m
V
Mass (kg)
Volume (m3
or L)
Density (kg/m3
)
 Most engineers and scientists use the greek letter
rho (ρ) to represent density.

8. 27.1 Densities of Common Materials
 Which materials are less dense than water?

9. 27.1 Properties of Solids
 The concept of physical
“strength” means the
ability of an object to hold
its form even when force is
applied.
 To evaluate the properties
of materials, it is
sometimes necessary to
separate out the effects of
design, such as shape
and size.

10. 27.1 Stress
 The stress in a material is the ratio of the force acting
through the material divided by the cross section area
through which the force is carried.
 The metric unit of stress is the pascal (Pa).
 One pascal is equal to one newton of force persquare
meterof area (1 N/m2
).
σ = F
A
Force (N)
Area (m2
)
Stress (N/m2
)

11. 27.1 Properties of Solids

12. 26.1 Properties of Solids
 A thicker wire can
support more force
at the same stress
as a thinner wire
because the cross
section area is
increased.

13. 26.1 Tensile strength
 The tensile strength is the stress at which a
material breaks under a tension force.
 The tensile strength
also describes how
materials break in
bending.

14. 27.1 Tensile strength

15. 27.1 Properties of solids
 The safety factor is the ratio of how strong
something is compared with how strong it has to
be.
 The safety factor allows for things that might
weaken the wire (like rust) or things you did not
consider in the design (like heavier loads).
 A safety factor of 10 means you choose the wire
to have a breaking strength of 10,000 newtons, 10
times stronger than it has to be.

16. 27.1 Evaluate 3 Designs
 Three designs have been proposed forsupporting a section of road.
 Each design uses three supports spaced at intervals along the road.
 A total of 4.5 million N of force is required to hold up the road.
 Evaluate the strength of each design.
 The factorof safety must be 5 orhighereven when the road is bumper-
to-bumperon all 4 lanes with the heaviest possible trucks.

17. 27.1 Evaluate Design #1
 High strength steel tubes
 Cross section = 0.015 m2
 Tensile strength = 600 Mpa

18. 27.1 Evaluate Design #2
 Aluminumalloy tubes
 Cross section = 0.015 m2
 Tensile strength = 290 Mpa

19. 27.1 Evaluate Design #3
 Steel cables
 Cross section = 0.03 m2
 Tensile strength = 400 Mpa

20. 27.1 Properties of solids
 Elasticity measures the ability of a material to
stretch.
 The strain is the amount a material has been
deformed, divided by its original size.

21. 27.1 Strain
 The Greek letter epsilon (ε) is usually used to
represent strain.
ε = ∆l
l
Change in
length (m)
Original length (m)
Strain

22. 27.1 Properties of solids
 The modulus of elasticity
plays the role of the
spring constant for solids.
 A material is elastic when
it can take a large
amount of strain before
breaking.
 A brittle material breaks
at a very low value of
strain.

23. 27.1 Modulus of Elasticity

24. 27.1 Stress forsolids
 Calculating stress forsolids is similarto using
Hooke's law forsprings.
 Stress and strain take the place of force and
distance in the formula:
σ = -E ε
Modulus of
elasticity (pa)
Strain
Stress (Mpa)

25. 27.1 Properties of solids
 The coefficient of thermal
expansion describes how much a
material expands foreach
change in temperature.
 Concrete bridges always have
expansion joints.
 The amount of contraction or
expansion is equal to the
temperature change times the
coefficient of thermal expansion.

26. 27.1 Thermal Expansion
∆l = α (T2-T1)
l
Change in
temperature (o
C)
Original length (m)
Coefficient of thermal expansionChange in
length (m)

27. 27.1 Thermal Expansion
 Which substances will
expand orcontract
the most with
temperature changes?

28. 27.1 Plastic
 Plastics are solids formed from long chain
molecules.
 Different plastics can have a wide range of
physical properties including strength, elasticity,
thermal expansion, and density.

29. 27.1 Metal
 Metals that bend and stretch easily without
cracking are ductile.
 The properties of metals can be changed by
mixing elements.
 An alloy is a metal that is a mixture of more than
one element.
 Steel is an alloy.

30. 27.1 Wood
 Many materials have different properties in
different directions.
 Wood has a grain that is created by the way trees
grow.
 Wood is very difficult to
break against the grain, but
easy to break along the
grain.
 A karate chop easily breaks
wood along its grain.

31. 27.1 Composite materials
 Composite materials are made
from strong fibers supported
by much weaker plastic.
 Like wood, composite
materials tend to be strongest
in a preferred direction.
 Fiberglass and carbon fiber
are two examples of useful
composite materials.

32. 27.2 Properties of Liquids and Fluids
Key Question:
What are some implications of Bernoulli’s equation?
*Students read Section 27.2 AFTER Investigation 27.2

33. 27.2 Properties of Liquids and Fluids
 Fluids can change shape and flow when forces
are applied to them.
 Gas is also a fluid because gases can change
shape and flow.
 Density, buoyancy and pressure are three
properties exhibited by liquids and gases.

34. 27.2 Density vs. Buoyancy
 The density of a liquid is the ratio of mass to
volume, just like the density of a solid.
 An object submerged in liquid feels an upward
force called buoyancy.
 The buoyancy force is exactly equal to the weight
of liquid displaced by the object.
 Objects sink if the buoyancy force is less than
their own weight.

36. 27.2 Pressure
 Forces applied to fluids
create pressure instead
of stress.
 Pressure is force per
unit area, like stress.
 A pressure of 1 N/m2
means a force of one
newton acts on each
square meter.

37. 27.2 Pressure
 Like stress, pressure is a ratio of force per unit
area.
 Unlike stress however, pressure acts in all
directions, not just the direction of the applied
force.

38. 27.2 Pressure
 The concept of pressure is
central to understanding how
fluids behave within
themselves and also how fluids
interact with surfaces, such as
containers.
 If you put a box with holes
underwater, pressure makes
waterflow in fromall sides.
 Pressure exerts equal force in
all directions in liquids that are
not moving.

39. 27.2 Properties of liquids and gases
 Gravity is one cause of
pressure because fluids
have weight.
 Air is a fluid and the
atmosphere of the Earth
has a pressure.
 The pressure of the
atmosphere decreases with
altitude.

40. 27.2 Properties of liquids and gases
 The pressure at any
point in a liquid is
created by the weight
of liquid above that
point.

41. 27.2 Pressure in liquids
 The pressure at the same depth is the same
everywhere in any liquid that is not moving.
P = ρ g d
Density (kg/m3
)
Depth (m)
Pressure
(pa or N/m2
)
Strength of gravity
(9.8 N/kg)

42. 27.2 Calculate pressure
 Calculate the pressure 1,000 meters
below the surface of the ocean.
 The density of wateris 1,000 kg/m3
.
 The pressure of the atmosphere is
101,000 Pa.
 Compare the pressure 1,000 meters
deep with the pressure of the
atmosphere.

43. 27.2 Properties of liquids and gases
 Pressure comes from collisions between atoms or
molecules.
 The molecules in fluids (gases and liquids) are not bonded
tightly to each otheras they are in solids.
 Molecules move around and collide with each otherand
with the solid walls of a container.

44. 27.2 Pressure and forces
 Pressure creates force on surfaces.
 The force is equal to the pressure times the area
that contacts the molecules.
F = P A
Pressure (N/m2
)
Area (m2
)
Force
(N)

45. 27.2 Calculate pressure
 A car tire is at a pressure of
35 psi.
 Four tires support a car that
weighs 4,000 pounds.
 Each tire supports 1,000
pounds.
 How much surface area of
the tire is holding up the
car?

46. 27.2 Motion of fluids
 The study of motion of fluids is called fluid
mechanics.
 Fluids flow because of differences in pressure.
 Moving fluids usually do not have a single speed.

47. 27.2 Properties of liquids and gases
 A flow of syrup down a
plate shows that
friction slows the syrup
touching the plate.
 The top of the syrup
moves fastest because
the drag from friction
decreases away from
the plate surface.

48. 27.2 Properties of liquids and gases
 Pressure and energy
are related.
 Differences in
pressure create
potential energy in
fluids just like
differences in height
create potential
energy from gravity

49. 27.2 Properties of liquids and gases
 Pressure does work as
fluids expand.
 A pressure of one
pascal does one joule
of work pushing one
square meter a
distance of one meter.

50. 27.2 Energy in fluids
 The potential energy is equal to volume times
pressure.
E = P V
Pressure (N/m2
)
Volume (m3
)
Potential
energy
(J)

51. 27.2 Energy in fluids
 The total energy of a small mass of fluid is equal
to its potential energy from gravity (height) plus its
potential energy from pressure plus its kinetic
energy.

52. 27.2 Energy in fluids
 The law of conservation of
energy is called Bernoulli’s
equation when applied to
a fluid.
 Bernoulli’s equation says
the three variables of
height, pressure, and
speed are related by
energy conservation.

53. 27.2 Bernoulli's Equation
 If one variable increases, at least one of the othertwo
must decrease.
 If the fluid is not moving (v =0), then Bernoulli’s equation
gives us the relationship between pressure and depth
(negative height).

54. 27.2 Properties of liquids and gases
 Streamlines are imaginary lines drawn to show
the flow of fluid.
 We draw streamlines so that they are always
parallel to the direction of flow.
 Fluid does not flow across streamlines.

55. 27.2 Applying Bernoulli's equation
 The wings of airplanes are made in the shape of
an airfoil.
 Air flowing along the top of the airfoil (B) moves
faster than air flowing along the bottom of the
airfoil (C).

56. 27.2 Calculating speed of fluids
 Water towers create
pressure to make water
flow.
 At what speed will water
come out if the water
level in the tower is 50
meters higher than the
faucet?

57. 27.2 Fluids and friction
 Viscosity is caused by forces
that act between atoms and
molecules in a liquid.
 Friction in fluids also
depends on the type of flow.
 Water running from a faucet
can be either laminar or
turbulent depending on the
rate of flow.

58. 27.3 Properties of Gases
Key Question:
How much matter is
in a gas?
*Students read Section 27.3 AFTER Investigation 27.3

59. 27.3 Properties of Gases
 Air is the most important
gas to living things on the
Earth.
 The atmosphere of the
Earth is a mixture of
nitrogen, oxygen, water
vapor, argon, and a few
trace gases.

60. 27.3 Properties of Gases
 An object submerged in gas feels an upward
buoyant force.
 You do not notice buoyant forces from air
because the density of ordinary objects is so
much greater than the density of air.
 The density of a gas depends on pressure and
temperature.

61. 27.3 Boyle's Law
 If the mass and temperature are kept constant, the
product of pressure times volume stays the same.
P1V1 = P2V2
Original volume (m3
)
Original pressure
(N/m2
)
Final pressure (N/m2
)
Final volume (m3
)

62. 27.3 Calculate using Boyle's law
 A bicycle pump creates
high pressure by squeezing
airinto a smallervolume.
 If airat atmospheric
pressure (14.7 psi) is
compressed froman initial
volume of 30 cubic inches
to a final volume of three
cubic inches, what is the
final pressure?

63. 27.3 Charles' Law
 If the mass and volume are kept constant, the pressure
goes up when the temperature goes up.
Original temperture
(k)
Original pressure
(N/m2
)
Final pressure (N/m2
)
Final temperature
(K)
P1 = P2
T1 T2

64. 27.3 Calculate using Charles' law
 A can of hairspray has a pressure
of 300 psi at room temperature
(21°C or294 K).
 The can is accidentally moved too
close to a fire and its
temperature increases to 800°C
(1,073 K).
 What is the final pressure in the
can?

65. 27.3 Ideal gas law
 The ideal gas law combines the pressure, volume,
and temperature relations for a gas into one
equation which also includes the mass of the gas.
 In physics and engineering, mass (m ) is used for
the quantity of gas.
 In chemistry, the ideal gas law is usually written in
terms of the number of moles of gas (n) instead of
the mass (m ).

66. 27.3 Gas Constants
 The gas
constants are
different because
the size and
mass of gas
molecules are
different.

67. 27.3 Ideal gas law
 If the mass and temperature are kept constant, the
product of pressure times volume stays the same.
P V = m R T
Volume (m3
)
Pressure
(N/m2
)
gas constant (J/kgK)
Temperature (K)
Mass (kg)

68. 27.3 Calculate using Ideal gas law
 Two soda bottles contain the same
volume of airat different pressures.
 Each bottle has a volume of 0.002 m3
(two liters).
 The temperature is 21°C (294 K).
 One bottle is at a gauge pressure of
500,000 pascals (73 psi).
 The otherbottle is at a gauge
pressure of zero.
 Calculate the mass difference
between the two bottles.

69. Application: The Deep Water Submarine
Alvin