physics for the respiratory therapistproperties of gases (cont.) sgaseous diffusion movement of...

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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

Copyright © 2014 by Mosby, an imprint of

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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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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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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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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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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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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 (Cont.)


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States of Matter

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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.)

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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



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Gas

Solid

Liquid

Energ

y o

f syste

m

melting

vaporization

sublimation

condensation

freezing

deposition


S Evaporation – liquid to gaseous state

S Condensation – gas to liquid

S Both essential components in respiration


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S Critical temperature

S Critical pressure

S Gases versus vapors


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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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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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Physical Properties of Matter

S Temperature

S Pressure

S Density

S Buoyancy

S Viscosity

S Surface Tension


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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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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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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

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Temperature Conversions


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Formulas

°C = 5/9 (°F – 32)

°F = (9/5 x °C) + 32

K = °C + 273


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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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Pressure Conversion: Units

S cm H2O

S mm Hg

S psi (lb/in2)

S atm

S kPa


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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


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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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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


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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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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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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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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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S Surface tension: cohesive forces

S Attractive forces between like kinds of molecules


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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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Change of State (cont.)

37

Change of State (cont.)

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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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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

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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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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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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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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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Combined Gas Law


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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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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.

Copyright © 2014 by Mosby, an imprint

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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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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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


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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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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

Flow Patterns


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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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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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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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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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