1. Chapter 6 Basic Physics for the Respiratory Therapist
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2. Learning Objectives
 Describe the properties that characterize the three states of matter.
 Describe how heat transfer occurs among substances.
 Identify the three common temperature scales and explain how to use them.
 Describe how substances undergo change of state.

3. Learning Objectives (cont.)
 Identify the factors that influence the vaporization of water.
 Describe how water vapor capacity, absolute humidity, and relative humidity are related.
 Describe how to predict gas behavior under changing conditions, including at extremes of temperature and pressure.
 Describe the principles that govern the flow of fluids.

4. Lecture Outline Energy and matter States of matter
Physical properties of liquids and gases
Gas laws
Fluid mechanics
Principles of electricity
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5. Physics
 Branch of science that deals with interaction of matter and energy
 Fields that make up physics:
 Mechanics
 Optics
 Acoustics
 Electricity
 Magnetism
 Thermodynamics
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6. Energy and Work 1 meter  Work is product of force and distance
 Energy and work are expressed in joules (J)
 One joule is force required to move 1 kilogram
1 meter
 Power measures rate at work being performed
 Watts (W) is unit of measure for power
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7. Energy and Matter  Energy is the ability to do work  Types of energy
 Mechanical
 Thermal
 Chemical
 Sound
 Nuclear
 Electrical
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8. Energy and Matter (Cont.)
 Law of conservation of energy
 Energy cannot be created or destroyed, only transferred
 Work = transfer of energy by mechanical means
 Mechanical energy
 Kinetic energy
 Potential energy
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9. Types of Energy  Kinetic energy – associated with movement
 Potential energy – amount of energy an object has due to its position
 When coal is burned, its potential energy is released
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10. Energy and Matter (Cont.)
 Kinetic energy = ½ (mv2)  Potential energy = mgh
(mass, force of gravity,
(mass,velocity)
 Examples
 Breaking of chemical bonds
 Hitting a ball
 Burning of fuel
 Water over a falls
height of the object)
 Examples
 Coiled spring
 Stretched rubber band
 Bicycle at top of hill
 Ice before it melts
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11. States of Matter  Matter – anything that has mass and occupies space
 Matter – Composed of atoms (elements)
 Atoms combine to form molecules – compounds/mixtures
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12. States of Matter (Cont.)
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13. States of Matter  Solids, Liquids, Gases  Solids
 Have high degree of internal order
 Fixed volume and shape
 Strong mutual attractive force between atoms
 Molecules have the shortest distance to travel before collision
 This motion referred to as a “jiggle”

14. States of Matter (cont.)
 Liquids
 Have fixed volume, but adapt to shape of their container
 Atoms exhibit less degree of mutual attraction compared w/ solids
 Shape is determined by numerous internal & external forces
 Gases
 No fixed volume or shape; weak attractive forces
 Gas molecules exhibit rapid, random motion w/ frequent
collisions

15. States of Matter (Cont.)
Gas
condensation
vaporization
deposition
sublimation
Liquid
Energy of system
melting
freezing
Solid
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16. States of Matter (Cont.)
 Evaporation – liquid to gaseous state
 Condensation – gas to liquid
 Both essential components in respiration
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17. States of Matter (Cont.)
 Critical temperature
 Critical pressure
 Gases versus vapors
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18. States of Matter (Cont.)
 Vapor exists below critical temperature
 May go back and forth when pressure is applied
 Above critical temperature true gas exists
 Most common vapors – H2O, CO2, and N2O
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19. States of Matter (Cont.)
 True gas exists above its critical temperature
 Cannot be converted to a liquid no matter how much
pressure is applied
 Examples: Air, O2, and He
 Water between 100°C on 374°C can be converted back from steam to liquid by applying high pressure.
 >374°C water can exist only as a gas was no matter how much pressure is applied
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20. Physical Properties of Matter
 Temperature
 Pressure
 Density
 Buoyancy
 Viscosity
 Surface Tension
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21. Temperature
 The measure of average kinetic energy of molecules in an object
 Thermometers are used to measure temperature
 Types of thermometers
 Nonelectrical
 Electrical
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22. Types of Thermometers
 Mercury thermometer – best example of nonelectrical thermometer
 Electrical thermometer – works on principle that resistance of metal increases with temperature
 Example of electrical: thermistor – resistance changes with changes in temperature. It is used with physiologic monitoring
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23. Temperature Scales  Temperature Scales
 Fahrenheit (F) & Celsius (C) scales based on property of water
 0° C is freezing point of water
 - 273° C = kinetic molecular activity stops = 0° K
 Kelvin scale (° K ) based on molecular motion
 Used by SI (Systeme Internationale) units
 Zero point = to absolute zero

24. Temperature Conversions
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25. Formulas °C = 5/9 (°F – 32) °F = (9/5 x °C) + 32 K = °C + 273
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26. 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
°F = ? k
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27. Pressure Conversion: Units
 cm H2O
 mm Hg
 psi (lb/in2)
 atm
 kPa
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28. Pressure Conversions = kPa  cm H2O x 0.7355 = mm Hg  cm H2O x 0.098
 mm Hg  760 = atm
 atm x = psi
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29. Practice Pressure Conversions
25 cm H2O = ? mm Hg
30 cm H2O = ? mm Hg
90 mm Hg = ? cm H2O
760 mm Hg = ? cm H2O
760 mm Hg = ? kPa
2 atm = ? mm Hg
2000 psi = ? atm
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30. Density  Defined as mass per unit of volume  D = mass/volume
 Solids are the most dense
 Gases are the least dense
 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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31. Buoyancy
 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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32. Viscosity cohesive forces between its molecules. easily
 Defined as force opposing fluid flow
 The viscosity of a fluid is directly proportional to the
cohesive forces between its molecules.
 Oil at low temperature has high viscosity
 As it is heated its viscosity decreases and it flows more
easily
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33. Physical Properties of Liquids and Gases
 Cohesion & adhesion
 Attractive force between like molecules = cohesion
 Attractive force between unlike molecules = adhesion
 Surface tension: Force exerted by like molecules at
liquid’s surface (why bubbles retain spherical shape)
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34. Physical Properties of Liquids and Gases (Cont.)
 Surface tension: adhesive forces
 Attractive forces between two different kinds of molecules
 Example: water and glass
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35. Physical Properties of Liquids and Gases (Cont.)
 Surface tension: cohesive forces
 Attractive forces between like kinds of molecules
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36. Physical Properties of Liquids and Gases (Cont.)
 LaPlace’s Law
 Pressure within a sphere is directly related to the surface tension of the liquid and inversely related to the radius of the sphere
 P = 2 (ST/r)
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37. Change of State (cont.)

38. Change of State (cont.)

39. The Gas Laws Pressure  Boyle’s Law  Avogadro’s Law  Charles’s Law
 Graham’s Law
 Gay-Lussac’s Law
 Fick’s Law of Diffusion
 Combined Gas Law
 Dalton’s Law of Partial
Pressure
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40. Properties of Gases frequent collisions  Kinetic activity of gases
 Gas molecules travel at high speeds in random fashion w/
frequent collisions
 Velocity of gas molecules is directly proportional to its temperature

41. Properties of Gases (cont.)
 Gaseous diffusionmovement of molecules from areas of high concentration to areas of lower concentration
 Gas pressure
 All gases exert pressure
 Gas pressure in a liquid is known as gas “tension”
 Atmospheric pressure is measured with a barometer
 Partial pressure = pressure exerted by single gas in gas mixture

42. Boyle’s Law  Temperature is constant
 Gas volume is inversely proportional to the absolute pressure exerted on it
 PV = k
 V1P1 = V2P2
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43. Charles’s Law  Pressure is constant
 Volume of gas varies directly with the temperature of the gas
 V / T = k
 V1 / T 1 = V2 / T2
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44. Gay-Lussac’s Law  Volume is constant
 Pressure varies directly with the absolute temperature of the gas
 P / T = k
 P1 / T1 = P2 / T2
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45. Boyle’s Law PV = k Charles’s Law V / T = k Ideal Gas Law PV = nRT
P and V change n,
R, T are constant
T and V change P,
n, R are constant
Ideal
Gas Law
PV = nRT
P, V, and T change n and R are constant
Combined
Gas Law
PV / T = k
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46. Combined Gas Law Copyright © 2014 by Mosby, an imprint of
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47. 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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48. Solubility of gases in liquids (Henry’s law)
 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.
 Solubility of gases in liquids (Henry’s law)
 Volume of gas dissolved in a liquid is a function of its solubility coefficient & its partial pressure
 Gases can dissolve in liquids.
Carbonated water and soda are good examples of a gas (CO2) dissolved in a liquid (water).
 Temperature plays a major role in gas solubility. High temperatures decrease solubility, and low temperatures increase solubility.
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
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49. Avogadro’s Law 6.02 x 1023 molecules
 Equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules
 1 gram molecular weight (gmw) = 1 mole
 1 mole of any gas occupies 22.4 L at 0° C and contains
6.02 x 1023 molecules
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50. Avogadro’s Law Example
 1 mole of oxygen (mw = 32 g) occupies a volume of L and contains 6.02 x 1023 molecules when measured at 0° C
 Density (g/L) = gmw of gas / 22.4 L
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51. Graham’s Law  Diffusion is rate at which two gases mix
 Rates of diffusion of 2 gases are inversely proportional to the square root of their masses
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52. Graham’s Law (Cont.) r1 / r2 = √d2 / d1
 Mass of a gas is directly proportional to its density at a constant temperature
r1 / r2 = √d2 / d1
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53. Fick’s Law of Diffusion
Many Molecules
Few Molecules
Resistance depends on the dimensions and properties of the membrane
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55. Fluid Mechanics  Flow patterns  Poiseuille’s law  Reynolds’ number
 Bernoulli principle
 Venturi principle
 Coanda phenomena
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56. Flow Patterns •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 56

57. Flow Patterns streamlines  Patterns of flow
 Laminar flowfluid moving in discrete cylindrical layers or
streamlines
 Poiseuille’s lawpredicts pressure required to produce given flow using ΔP = 8nl V./ πr4
 Turbulent flowloss of regular streamlines; fluid molecules form irregular eddy currents in chaotic pattern is predicted by using Reynold`s number (NR)
 NR = v d2r / h

58. Flow Patterns
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59. Poiseuille’s Law n viscosity, L length of tube, r radius of tube.
 Flow through a tube
 Q = (P1 – P2) / R(Resistance)
 Resistance to flow through a tube
 R = (8ήL) / (π r4)
n viscosity, L length of tube, r radius of tube.
 Note that decreasing the radius by one half increases the resistance 16 fold (Asthma)
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60. Reynolds’ Number
 Dimensionless number related to pattern of flow to
indicate whether fluid flow past a body or in a duct is steady or turbulent.
 NR = v × d × (2r/ή)
 V = velocity of flow
 r = radius of the tube
 d = density of the gas
 ή = viscosity
 NR >2000 means turbulent flow predominates
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61. Fluid Mechanics: Bernoulli
The Bernoulli effect
 Fluid passing through tube that meets constriction
experiences significant pressure drop
 Fluid that flows through constriction increases its velocity while lateral wall pressure decreases
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62. 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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63. Fluid Mechanics Fluid entrainment
 Velocity of fluid (gas) can increase greatly at point of constriction
 Causing lateral pressure to fall below atmospheric pressure
 If open tube is placed distal to constriction, another fluid can be pulled into primary flow stream (fluid entrainment)
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64. Fluid Mechanics: Venturi (Cont.)
This design helps keep the percentage of entrained fluid
constant, even when the total flow varies.
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65. Fluid Mechanics Fluidics & Coanda effect
 Fluidics is branch of engineering applying hydrodynamics principles in flow circuits
 Coanda effect (wall attachment) is observed when fluid flows through small orifice w/ properly contoured downstream surfaces
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66. Fluid Mechanics: Coanda Effect (Cont.)
 Add contoured tube distal to the constriction and the gas will adhere to the wall of the contoured tube because:
 Negative pressure past constriction draws fluid toward the curved extension
 Ambient pressure pushes the fluid stream against the wall
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