Applied Physics
RET 2274
Respiratory Therapy Theory I
Module 1.0
States of Matter

Three Primary States of Matter
Solid
Liquid
Gas
States of Matter

Solid

Atoms are kept in
place by strong
mutual attractive
forces and are
limited to backand-forth motion
about a central
position
States of Matter

Liquid

Atoms are kept in place
by mutual attraction
(much weaker than that
of solids) and can
move about freely and
can take the shape of
their container –
capable of flow. Like
solids, liquids are
dense and cannot
easily be compressed
States of Matter

Gas

Molecular attractive forces
are very weak and their
movement is rapid and
random with frequent
collisions. Gases have no
inherent boundaries and
are easily compressed and
expanded. Like liquids,
gases can flow. Liquids
and gases are considered
fluids.
Temperature Scales

Absolute Zero


The concept that a temperature exists at which there
is no kinetic energy (energy of motion) – exists in
theory only
Kelvin (K)



Zero degrees K = absolute zero
Freezing point of water = 273 K
Boling point of water = 373 K
Temperature Scales

Celsius (C)


Freezing point of water = 0º C
Boiling point of water = 100º C

Note: To covert degrees Celsius to degrees
Kelvin, simply add 273
Example: 25º C = 25 + 273 = 298º K
Temperature Scales

Fahrenheit


Freezing point of water = 32º F
Boiling point of water = 212º F

To covert degrees Fahrenheit to degrees Celsius, use
the following formula
ºC = 5/9 (ºF – 32)

To covert degrees Celsius to degrees Fahrenheit, use
the following formula
ºF = (9/5 x ºC) + 32
Temperature Scales

Linear relationship between gas molecular activity, or pressure,
and temperature. The graph shows comparable readings on
three scales for five temperature points
Freezing point
of water
Boiling point
of water
Change of State

Liquid-Solid Phase Changes

The changeover from the solid to liquid state is called
MELTING

The temperature at which solid change to liquid is called
the MELTING POINT
Change of State

Liquid-Solid Phase Changes

The changeover from the liquid to solid state is called
FREEZING; it is the opposite of melting

The FEEZING POINTS and MELTING POINTS of a
substance are the same
Change of State

Liquid-Vapor Phase Changes

As the temperature of a liquid increases, its state changes
to VAPOR
Change of State

Liquid-Vapor Phase Changes

This change of state is called VAPORIZATION

Two different forms of vaporization
BBOILING
EVAPORATION
Change of State

Liquid-Vapor Phase Changes

Boiling occurs at the BOILING POINT

The boiling point of a liquid is the
temperature at which its vapor
pressure equals atmospheric
pressure – its molecules must have
enough kinetic energy to force
themselves into the atmosphere
against the opposing pressure
Change of State

Liquid-Vapor Phase Changes

Boiling occurs at the BOILING POINT

The boiling point of liquid oxygen at 1
atmosphere pressure is -183º C
Change of State

Liquid-Vapor Phase Changes

EVAPORATION is when a liquid
changes into a gas at temperatures
lower than its boiling point

After water is converted to a vapor, it
acts like any gas. This invisible
gaseous form of water is called
MOLECULAR WATER
Change of State

Liquid-Vapor Phase Changes

When a gas is fully saturated with
water vapor, slight cooling of the gas
causes its water vapor to turn back
into the liquid state, a process called
CONDENSATION

The temperature at which
condensation begins is called the
DEW POINT
Changes of State

Critical Temperature


The highest temperature
at which a substance
can exist as a liquid
Critical Pressure

The pressure needed to
maintain equilibrium
between the liquid and
gas phases of a
substance at its critical
temperature
A typical phase diagram. The dotted
green line gives the anomalous
behavior of water
Phase Diagram
Properties of Liquids

Pressure in Liquids


Liquids exert pressure
The pressure exerted by a liquid depends on both its
height (depth) and weight density (weight per unit volume)
Pascal’s principle. Liquid pressure depends only on the height (h) and not on the shape of the
vessel or the total volume of liquid. (Modified from Nave CR, Nave BC: Physics for the health
sciences, ed 3, Philadelphia, 1985, WB Saunders.)
Properties of Liquids

Buoyancy

Liquids exert buoyant
force because the
pressure below a
submerged object
always exceeds the
pressure above it.

The upward buoyant
force will overcome
gravity, and the object
will float
Properties of Liquids

Buoyancy

Gases also exert
buoyant force, which
helps keep solid
particles suspended
in gases
Blue and white smoke ascending
Properties of Liquids

Viscosity

Viscosity is the force
opposing a fluid’s flow;
viscosity in fluids is like
friction in solids

A fluids viscosity is
directly proportional to the
cohesive forces between
it molecules; the stronger
the cohesive forces, the
greater is the fluid’s
viscosity
Properties of Liquids

Viscosity

The greater a fluid’s viscosity, the greater is its
resistance to deformation and the greater is its
opposition to flow
Properties of Liquids

Viscosity

The greater the viscosity
of a fluid, the more
energy is needed to
make it flow

Example: When there is
an increase in red blood
cells (polycythemia), the
heart must work harder
to circulate the blood
because it is more
viscous
Properties of Liquids

Laminar Flow

When fluids move in discrete cylindrical layers called
streamlines
Properties of Liquids

Laminar Flow

The difference in the velocity among these concentric
layers is called shear rate

The pressure pushing or driving the fluid is called
shear stress
Properties of Liquids

Cohesion and Adhesion

The attractive force between like molecules is called
cohesion
Properties of Liquids

Cohesion and Adhesion

The attractive forces between unlike molecule is
adhesion
Properties of Liquids

Cohesion and Adhesion

The shape of the meniscus
depends on the relative
strengths of adhesion and
cohesion. A, Water; adhesion
stronger than cohesion. B,
Mercury; cohesion stronger
than adhesion
Properties of Liquids

Surface Tension

The force exerted by like molecules at a liquid’s
surface
Properties of Liquids

Surface Tension

The force of surface
tension in a drop of
liquid. Cohesive force
(arrows) attracts
molecules inside the
drop to one another.
Cohesion can pull the
outermost molecules
inward only, creating a
centrally directed force
that tends to contract
the liquid into a sphere
Properties of Liquids

Surface Tension

The lungs resemble
clumps of bubble, it
follows therefore that
surface tension plays a
key role in the mechanics
of ventilation

Abnormalities in alveolar
surface tension occur in
certain clinic conditions,
e.g., infant respiratory
distress syndrome
Properties of Liquids

Surface Tension

Laplace’s Law: In a liquid sphere, the pressure
required to distend the sphere is directly proportional to
the surface tension of the liquid and inversely
proportional to the sphere’s radius
Properties of Liquids

Surface Tension
Laplace’s relationship. Two bubbles
of different sizes with the same surface
tension. Bubble A, with the smaller
radius, has the greater inward or
deflating pressure and is more prone
to collapse than the larger bubble B.
Because the two bubbles are
connected, bubble A would tend to
deflate and empty into bubble B.
Conversely, because of bubble A’s
greater surface tension, it would be
harder to inflate than bubble B.
Equation for liquid bubble
P = 4ST
r
P = distending pressure
ST = surface tension
r = spherical radius
Properties of Gases

Gases share many properties with liquids

Gases:



Exert pressure
Capable of flow
Exhibit the properties of viscosity
However, unlike liquids, gases are readily compressed
and expanded and fill the spaces available to them
through diffusion
Properties of Gases

Gaseous Diffusion

Diffusion:The process whereby molecules move from
areas of high concentration to areas of lower
concentration

Kinetic Energy: The driving forced behind diffusion.
Because gases have high kinetic energy, they diffuse
most rapidly
Note: Because diffusion is based on kinetic activity, anything
that increases molecular activity will quicken diffusion, e.g.,
heating
Properties of Gases

Gaseous Diffusion

Graham’s Law: The rate of diffusion of a gas (D) is
inversely proportional to the square root of its density:

Lighter gases diffuse rapidly, whereas heavy gases
diffuse more slowly
Properties of Gases

Gas Pressure

Whether free in the atmosphere, enclosed in a
container, or dissolved in a liquid such as blood, all
gases exert pressure


In physiology, the term tension is often used to refer to
the pressure exerted by gases when dissolved in liquids
Pressure is a measure of force per unit area

PSI: Pounds per square inch (lb/in²)


British fps
N/m² : Newton per meter squared (Pascal)

International System of Units (SI)
Properties of Gases

Gas Pressure

Pressure can also be measured
indirectly as the height of column of
liquid:
Centimeters of water pressure (cm H2O)
Millimeters of mercury (mm Hg)

Both mercury and water columns are
still used in clinical practice, especially
when vascular pressures are being
measured
Properties of Gases

Partial Pressure (Dalton’s Law)

Many gases exist together as mixtures, for example
air, which contain mostly oxygen and nitrogen

The pressure exerted by a single gas is called its
partial pressure
PressureTotal = Pressure1 + Pressure2 ... Pressuren
Properties of Gases

Partial Pressure (Dalton’s Law
Partial Pressure = Fractional concentration x Total atmospheric pressure
Approximate Fractional Gas
Concentrations of Air
Partial Pressures of Gases in Air
PO2 = 0.21 x 760 torr =
160 torr
PN2 = 0.79 x 760 torr =
600 torr
Properties of Gases

Composition of Earth’s Atmosphere
Properties of Gases

Solubility of Gas in Liquids (Henry’s Law)

At a constant temperature, the solubility of a gas in a
liquid is proportional to the pressure of that gas above
the liquid
William Henry (chemist)
Properties of Gases

Solubility of Gas in Liquids (Henry’s Law)

Temperature plays an important role in gas solubility

High temperatures decrease solubility

Low temperatures increase solubility
Leave a carbonated drink open and out of
the refrigerator and it will quickly go flat
Gas Laws

Several laws help define the relationship
among gas pressure, temperature, mass,
and volume




Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
Combined Gas Law
Gas Laws

Boyle’s Law
Description
Constants
Working Formula
The volume of a gas
varies inversely with
its pressure
Temperature,
mass
P1V1 = P2V2
Gas Laws

Boyle’s Law
Gas Laws

Charles’ Law
Description
Constants
Working Formula
The volume of a gas
varies directly with
changes in its
temperature
Pressure,
mass
V1 = V2
T1 T2
Gas Laws

Charles’ Law
Gas Laws

Gay Lussac’s Law
Description
Constants
Working Formula
The pressure exerted
by a gas varies
directly with its
absolute temperature
Volume,
mass
P1 = P2
T1 T2
Gas Laws

Gay Lussac’s Law
Gas Laws

Combined Gas Law
Description
Constants
Working Formula
Interaction of the all
the gas laws
None
P1V1 = P2V2
T1
T2
Gas Laws

Combined Gas Law
P1V1 = P2V2
T1
T2
Gas Behavior Under Changing Conditions

Effects of Water Vapor

Water vapor, like any gas, occupies space

The dry volume of a gas at a constant pressure and
temperature is always smaller than it saturated
volume
Ptotal - Pwater vapor
=
Pdry gas
Gas Behavior Under Changing Conditions

Effects of Water Vapor

Correcting from the dry state to saturated state always
yields a larger gas volume
Pdry gas + Pwater vapor = Ptotal
Gas Behavior Under Changing Conditions

Effects of Water Vapor

Addition of water vapor to a gas mixture always
lowers the partial pressures of the other gases
present
Pc = Fgas x (PT – PH2O)
Pc = Corrected gas pressure
Fgas = The fractional concentration of gas in the mixture
P = The water vapor pressure at a given temperature
Gas Behavior Under Changing Conditions

Critical Temperature


The highest temperature
at which a substance
can exist as a liquid
Critical Pressure

The pressure needed to
maintain equilibrium
between the liquid and
gas phases of a
substance at its critical
temperature
A typical phase diagram. The dotted
green line gives the anomalous
behavior of water
Gas Behavior Under Changing Conditions

Phase Diagram
Fluid Dynamics

Both liquids and gases can flow

Flow is the bulk movement of a substance through
space
Flow = Movement of a volume per unit of time
= L/minute
Fluid Dynamics

Pressures in Flowing Fluids

Flow Resistance

Available energy decreases because frictional forces
(fluid viscosity, tube wall) oppose fluid flow
R = (P1 – P2)
Fluid Dynamics

Patterns of Flow

Laminar Flow

Turbulent

Transitional
Fluid Dynamics

Patterns of Flow

Laminar Flow

During laminar flow a fluid moves in discrete cylindrical
layers or streamlines
Fluid Dynamics

Patterns of Flow

Laminar Flow

Poiseuille’s Law: For fluids flowing in a laminar pattern,
the driving pressure will increase whenever the fluid
viscosity, tube length, or flow increases; greater
pressure is required to maintain a given flow if the tube
radius is decreased
P = 8nl _
r4
Fluid Dynamics

Patterns of Flow

Turbulent Flow

Under certain conditions, fluid molecules may form
irregular eddy currents in a chaotic pattern called
turbulent flow
Fluid Dynamics

Patterns of Flow

Turbulent Flow

Reynold’s Number
 >3000 = Turbulent
 2000 – 3000 = Transitional
 <2000 = Laminar
Fluid Dynamics

Patterns of Flow

Transitional Flow

Mixture of laminar and turbulent flow

Flow in the respiratory tract is mainly transitional
Fluid Dynamics

The Bernoulli Effect

As a fluid flows through a constriction, its
velocity increases and its lateral pressure
decreases
Fluid Dynamics

The Bernoulli Effect

According to the Bernoulli theorem, a flowing fluid’s lateral
pressure must vary inversely with its velocity. a, Flow in tube
“a”; va, velocity in tube “a”; vb, velocity in tube “b”; b, flow in
tube “b”; Pa, lateral wall pressure in tube “a”; Pb, lateral wall
pressure after restriction
Fluid Dynamics

Fluid Entrainment

When a flowing fluid encounters a very narrow passage, its
velocity can increase greatly and cause the fluid’s lateral
pressure to fall below that exerted by the atmosphere and
pull another fluid into the primary flow stream
Fluid Dynamics

Fluid Entrainment

The amount of air
entrained depends on
both the diameter of
the jet orifice and the
size of the air
entrainment ports
Fluid Dynamics

Fluids and the Coanda Effect

The amount of air entrained depends on both the
diameter of the jet orifice and the size of the air
entrainment ports
Fluid Dynamics

Fluids and the Coanda Effect

Is the tendency of a fluid jet to stay
attached to an adjacent curved
surface that is very well shaped