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S
Chapter 6Basic Physics for the
Respiratory Therapist
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Learning Objectives
2
S Describe the properties that characterize the three states of
matter.
S Describe how heat transfer occurs among substances.
S Identify the three common temperature scales and explain
how to use them.
S Describe how substances undergo change of state.
Learning Objectives (cont.)
S Identify the factors that influence the vaporization of water.
S Describe how water vapor capacity, absolute humidity, and relative humidity are related.
S Describe how to predict gas behavior under changing conditions, including at extremes of temperature and pressure.
S Describe the principles that govern the flow of fluids.
3
Lecture Outline
Energy and matter
States of matter
Physical properties of liquids and gases
Gas laws
Fluid mechanics
Principles of electricity
Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 4
Physics
S Branch of science that deals with interaction of matter and energy
S Fields that make up physics:
S Mechanics
S Optics
S Acoustics
S Electricity
S Magnetism
S Thermodynamics
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Elsevier Inc.5
Energy and Work
S Work is product of force and distance
S Energy and work are expressed in joules (J)
S One joule is force required to move 1 kilogram
1 meter
S Power measures rate at work being performed
S Watts (W) is unit of measure for power
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Elsevier Inc.6
Energy and Matter
S Energy is the ability to do work
S Types of energy
S Mechanical
S Thermal
S Chemical
S Sound
S Nuclear
S Electrical
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Elsevier Inc.7
Energy and Matter (Cont.)
S Law of conservation of energy
S Energy cannot be created or destroyed, only transferred
S Work = transfer of energy by mechanical means
S Mechanical energy
S Kinetic energy
S Potential energy
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Elsevier Inc.8
Types of Energy
S Kinetic energy – associated with movement
S Potential energy – amount of energy an object has due to
its position
S When coal is burned, its potential energy is released
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Elsevier Inc.9
Energy and Matter (Cont.)
S Kinetic energy = ½ (mv2)
(mass,velocity)
S ExamplesS Breaking of chemical bonds
S Hitting a ball
S Burning of fuel
S Water over a falls
S Potential energy = mgh
(mass, force of gravity,
height of the object)
S ExamplesS Coiled spring
S Stretched rubber band
S Bicycle at top of hill
S Ice before it melts
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Elsevier Inc.10
States of Matter
S Matter – anything that has mass and occupies space
S Matter – Composed of atoms (elements)
S Atoms combine to form molecules – compounds/mixtures
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States of Matter
13
S Solids, Liquids, Gases
S Solids
S Have high degree of internal order
S Fixed volume and shape
S Strong mutual attractive force between atoms
S Molecules have the shortest distance to travel before
collision
S This motion referred to as a “jiggle”
States of Matter (cont.)
14
S Liquids
S Have fixed volume, but adapt to shape of their container
S Atoms exhibit less degree of mutual attraction compared w/
solids
S Shape is determined by numerous internal & external forces
S Gases
S No fixed volume or shape; weak attractive forces
S Gas molecules exhibit rapid, random motion w/ frequent
collisions
States of Matter (Cont.)
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Elsevier Inc.15
Gas
Solid
Liquid
Energ
y o
f syste
m
melting
vaporization
sublimation
condensation
freezing
deposition
States of Matter (Cont.)
S Evaporation – liquid to gaseous state
S Condensation – gas to liquid
S Both essential components in respiration
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Elsevier Inc.16
States of Matter (Cont.)
S Critical temperature
S Critical pressure
S Gases versus vapors
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Elsevier Inc.17
States of Matter (Cont.)
S Vapor exists below critical temperature
S May go back and forth when pressure is
applied
S Above critical temperature true gas exists
S Most common vapors – H2O, CO2, and
N2O
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Elsevier Inc.18
States of Matter (Cont.)
S True gas exists above its critical temperature
S Cannot be converted to a liquid no matter how much
pressure is applied
S Examples: Air, O2, and He
S Water between 100°C on 374°C can be converted back
from steam to liquid by applying high pressure.
S >374°C water can exist only as a gas was no matter how
much pressure is applied
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Elsevier Inc.19
Physical Properties of Matter
S Temperature
S Pressure
S Density
S Buoyancy
S Viscosity
S Surface Tension
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Elsevier Inc.20
Temperature
S The measure of average kinetic energy of molecules in
an object
S Thermometers are used to measure temperature
S Types of thermometers
S Nonelectrical
S Electrical
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Elsevier Inc.21
Types of Thermometers
S Mercury thermometer – best example of nonelectrical
thermometer
S Electrical thermometer – works on principle that
resistance of metal increases with temperature
S Example of electrical: thermistor – resistance changes
with changes in temperature. It is used with physiologic
monitoring
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Elsevier Inc.22
Temperature Scales
S Temperature Scales
S Fahrenheit (F) & Celsius (C) scales based on property of
water
S 0° C is freezing point of water
S - 273° C = kinetic molecular activity stops = 0° K
S Kelvin scale (° K ) based on molecular motion
S Used by SI (Systeme Internationale) units
S Zero point = to absolute zero
23
Formulas
°C = 5/9 (°F – 32)
°F = (9/5 x °C) + 32
K = °C + 273
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Elsevier Inc.25
Practice Temperature
Conversions
1. 25°C = ?°F
2. 35°C = ?°F
3. 37°C = ?°F
4. 39°C = ?°F
5. 39°C = ? k
6. 70°F = ?°C
7. 78°F = ?°C
8. 90°F = ?°C
9. 103°F = ?°C
10. 103°F = ? k
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Elsevier Inc.26
Pressure Conversion: Units
S cm H2O
S mm Hg
S psi (lb/in2)
S atm
S kPa
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Elsevier Inc.27
Pressure Conversions
S cm H2O x 0.7355 =mm Hg
S cm H2O x 0.098 =kPa
S mm Hg 760 = atm
S atm x 14.7 = psi
Copyright © 2014 by Mosby, an imprint of
Elsevier Inc.28
Practice Pressure Conversions
1. 25 cm H2O = ? mm Hg
2. 30 cm H2O = ? mm Hg
3. 90 mm Hg = ? cm H2O
4. 760 mm Hg = ? cm H2O
5. 760 mm Hg = ? kPa
6. 2 atm = ? mm Hg
7. 2000 psi = ? atm
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Elsevier Inc.29
Density
S Defined as mass per unit of volume
S D = mass/volume
S Solids are the most dense
S Gases are the least dense
S A block of wood is much more dense than a block of Styrofoam, if both are the same size; Styrofoam is much more likely to float
Copyright © 2014 by Mosby, an imprint of
Elsevier Inc.30
Buoyancy
S When an object is submerged in water it will be buoyed
up by a force equal to the weight of water displaced by
the weight of fluid that is displaced by the object
(Archimedes Principle)
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Elsevier Inc.31
Viscosity
S Defined as force opposing fluid flow
S The viscosity of a fluid is directly proportional to the
cohesive forces between its molecules.
S Oil at low temperature has high viscosity
S As it is heated its viscosity decreases and it flows more
easily
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Elsevier Inc.32
Physical Properties of
Liquids and Gases
S Cohesion & adhesion
S Attractive force between like molecules = cohesion
S Attractive force between unlike molecules = adhesion
S Surface tension: Force exerted by like molecules at
liquid’s surface (why bubbles retain spherical shape)
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Elsevier Inc.33
Physical Properties of
Liquids and Gases (Cont.)
S Surface tension: adhesive forces
S Attractive forces between two different kinds of molecules
S Example: water and glass
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Elsevier Inc.34
Physical Properties of
Liquids and Gases (Cont.)
S Surface tension: cohesive forces
S Attractive forces between like kinds of molecules
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Elsevier Inc.35
Physical Properties of
Liquids and Gases (Cont.)
S LaPlace’s Law
S Pressure within a sphere is directly related to the surface
tension of the liquid and inversely related to the radius of the
sphere
S P = 2 (ST/r)
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Elsevier Inc.36
The Gas Laws
S Boyle’s Law
S Charles’s Law
S Gay-Lussac’s Law
S Combined Gas Law
S Dalton’s Law of Partial
Pressure
S Avogadro’s Law
S Graham’s Law
S Fick’s Law of Diffusion
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Elsevier Inc.39
40
Properties of Gases
S Kinetic activity of gases
S Gas molecules travel at high speeds in random fashion w/
frequent collisions
S Velocity of gas molecules is directly proportional to its
temperature
41
Properties of Gases (cont.)
S Gaseous diffusionmovement of molecules from areas
of high concentration to areas of lower concentration
S Gas pressure
S All gases exert pressure
S Gas pressure in a liquid is known as gas “tension”
S Atmospheric pressure is measured with a barometer
S Partial pressure = pressure exerted by single gas in gas
mixture
Boyle’s Law
S Temperature is constant
S Gas volume is inversely
proportional to the
absolute pressure
exerted on it
S PV = k
S V1P1 = V2P2
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Elsevier Inc.42
Charles’s Law
S Pressure is constant
S Volume of gas varies
directly with the
temperature of the
gas
S V / T = k
S V1 / T 1 = V2 / T2
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Elsevier Inc.43
Gay-Lussac’s Law
S Volume is constant
S Pressure varies directly with
the absolute temperature of
the gas
S P / T = k
S P1 / T1 = P2 / T2
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Elsevier Inc.44
Boyle’s Law
PV = k
Charles’s Law
V / T = k
Ideal
Gas Law
PV = nRT
Combined
Gas Law
PV / T = k
P and V change n, R, T are constant
T and V change P, n, R are constant
P, V, and T change n and R are constant
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Elsevier Inc.45
Dalton’s Law of Partial
Pressure
Dalton’s law partial
pressure of gas in mixture is
proportional to its percentage in
mixture
The sum of the partial
pressures of the individual
gases.
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Elsevier Inc.47
Solubility of gases in liquids
(Henry’s law)
S Solubility of gases in liquids (Henry’s law)
S Volume of gas dissolved in a liquid is a function of its solubility coefficient & its partial pressure
S Gases can dissolve in liquids. Carbonated water and soda are good examples of a gas (CO2) dissolved in a liquid (water).
S The solubility coefficient equals
the volume of a gas that will
dissolve in 1 ml of a given liquid at
standard pressure and specified
temperature.
S Temperature plays a major role in
gas solubility. High temperatures
decrease solubility, and low
temperatures increase solubility.
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of Elsevier Inc.48
The effect of temperature on solubility is a result of changes in kinetic activity.
As a liquid is warmed, the kinetic activity of any dissolved gas molecules is
increased
Avogadro’s Law
S Equal volumes of gases, at the same temperature and
pressure, contain equal numbers of molecules
S 1 gram molecular weight (gmw) = 1 mole
S 1 mole of any gas occupies 22.4 L at 0° C and contains
6.02 x 1023 molecules
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Elsevier Inc.49
Avogadro’s Law Example
S 1 mole of oxygen (mw = 32 g) occupies a volume of 22.4
L and contains 6.02 x 1023 molecules when measured at
0° C
S Density (g/L) = gmw of gas / 22.4 L
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Elsevier Inc.50
Graham’s Law
S Diffusion is rate at which two gases mix
S Rates of diffusion of 2 gases are inversely proportional to
the square root of their masses
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Graham’s Law (Cont.)
S Mass of a gas is directly proportional to its density at a
constant temperature
r1 / r2 = √d2 / d1
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Fick’s Law of Diffusion
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Many Molecules Few Molecules
Resistance depends on the
dimensions and properties of the
membrane
Fluid Mechanics
S Flow patterns
S Poiseuille’s law
S Reynolds’ number
S Bernoulli principle
S Venturi principle
S Coanda phenomena
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Elsevier Inc.55
Flow Patterns
56
•Study of fluids in motion = hydrodynamics
•Pressure exerted by liquid in motion depends on nature
of flow itself
•Progressive decrease in fluid pressure occurs as fluid
flows through tube due to resistance
Flow Patterns
57
S Patterns of flow
S Laminar flowfluid moving in discrete cylindrical layers or
streamlines
S Poiseuille’s lawpredicts pressure required to produce given
flow using ΔP = 8nl V./ πr4
S Turbulent flowloss of regular streamlines; fluid molecules
form irregular eddy currents in chaotic pattern is predicted by
using Reynold`s number (NR)
S NR = v d2r / h
Poiseuille’s Law
S Flow through a tube
S Q = (P1 – P2) / R(Resistance)
S Resistance to flow through a tube
S R = (8ήL) / (π r4)
n viscosity, L length of tube, r radius
of tube.
S Note that decreasing the radius by
one half increases the resistance 16
fold (Asthma)
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Reynolds’ Number
S Dimensionless number related to pattern of flow to indicate whether fluid flow past a body or in a duct is steady or turbulent.
S NR = v × d × (2r/ή)S V = velocity of flow
S r = radius of the tube
S d = density of the gas
S ή = viscosity
S NR >2000 means turbulent flow predominates
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Elsevier Inc.60
Fluid Mechanics: Bernoulli
• The Bernoulli effect
S Fluid passing through tube that meets constriction
experiences significant pressure drop
S Fluid that flows through constriction increases its velocity
while lateral wall pressure decreases
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Fluid Mechanics: Venturi
The pressure drop that occurs distal to the constriction in a
tube can be restored to the pre-constriction pressure if there
is a dilation in the tube distal to the constriction with an angle
of divergence not exceeding 15 degrees.
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Fluid Mechanics
• Fluid entrainment
S Velocity of fluid (gas) can increase greatly at point of
constriction
S Causing lateral pressure to fall below atmospheric pressure
S If open tube is placed distal to constriction, another fluid can
be pulled into primary flow stream (fluid entrainment)
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of Elsevier Inc.63
Fluid Mechanics: Venturi
(Cont.)
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This design helps keep the percentage of entrained fluid
constant, even when the total flow varies.
Fluid Mechanics
• Fluidics & Coanda effect
S Fluidics is branch of engineering applying hydrodynamics
principles in flow circuits
S Coanda effect (wall attachment) is observed when fluid flows
through small orifice w/ properly contoured downstream
surfaces
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of Elsevier Inc.65
Fluid Mechanics: Coanda Effect
(Cont.)
S Add contoured tube distal to the constriction and the gas will adhere to the wall of the contoured tube because:
S Negative pressure past constriction draws fluid toward the curved extension
S Ambient pressure pushes the fluid stream against the wall
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Elsevier Inc.66
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