Physics for Geologists, Second edition

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1 10 Acoustics: sound and other waves techniques for amplifying these signals. This is mainly achieved by having a long array of geophones, and moving the shot-point and the geophones between shots so that multiple reflections are received from the same subsur- face positions - the common depth points, or CDP as the method is called. This is a computer-dependent process, and we shall not pursue it further here. See Telford et al. (1990) for a more detailed exposition of seismic theory and practice - and indeed of the other geophysical methods of gravity and magnetic surveys. Copyright 2002 by Richard E. Chapman
12 Fluids and fluid flow Introduction Fluid flow is an important process in geology: it is also one of the least well understood, and the literature is full of errors. These errors arise mainly from ignorance and carelessness, as you would expect; but it is also a difficult subject. Its difficulty lies not so much in the mathematics involved as in the physical concepts. The fundamental cause of the error and its propagation is confusion between pressure and energy, and the erroneous statement that 'water flows from high pressure to low'. We saw in Chapter 3 examples of gravity-driven processes in which water flows from low pressure to high. General geology requires a good understanding of the principles of fluid flow for the various processes of sediment distribution (wind, water) and vol- canic activity. Groundwater geology and petroleum geology require a good understanding of the physics involved in fluid flow, but it is one of the tragedies of science that some of the definitions are erroneously stated. Ignore the fluid flow part of Jaeger and Cook's Fundamentals of rock mechanics in all three editions (I have a letter from Jaeger dated 26 April 1976 to this effect). The greatest tragedy is perhaps the erroneous or incomplete defin- ition of the darcy, the unit of permeability in petroleum studies. This also shows some of the complexity of the concepts because the four authors of the papers defining the darcy were physicists and mathematicians. Do not despair, even if your mathematics is weak, because it is not as difficult as all that. By the end of this chapter, the principles at least will be clear to you. If you watch the smoke rising from a cigarette in a still room, it rises first in a vertical straight line and then suddenly breaks up into eddies and whorls. Similarly, a stream may flow with a smooth upper surface until it narrows, where it breaks in rough water. The smooth flow is called laminar; the rough, turbulent. Laminar flow is amenable to general mathematical treatment: turbulent flow is more difficult. Consider water flowing in a channel of rectangular cross-section and gentle slope. The component of weight down the slope provides the force that accelerates the water. Frictional resistance on the bottom and the sides, and Copyright 2002 by Richard E. Chapman
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Physics for Geologists Second editi
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Copyright 2002 by Richard E. Chapma
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... vlii Contents Polarization 47 L
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Figures Copyright 2002 by Richard E
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Tables Copyright 2002 by Richard E.
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xiv Preface waves diminishes with d
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xvi Preface provides. This book is
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xviii Acknowledgements to K. Whaler
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xx Symbols mass refractive index bu
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2 Basic concepts Table 1.1 Dimensio
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4 Basic concepts Table 1.2 Basic SI
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6 Basic concepts pascal (Pa) and si
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8 Basic concepts all the relevant d
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10 Basic concepts relating them by
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2 Force The dimensions of force are
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14 Force The ratio of the Moon's ac
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16 Force Figure 2.1 The sum of the
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18 Force When a motorcycle takes a
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20 Force Figure 2.3 Torque is the p
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22 Force How does momentum differ f
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24 Force the weights - that is, the
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26 Force Figure 2.6 Wall-sticking i
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3 Gravity Universal gravity When di
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30 Gravity are significant to geolo
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32 Gravity Figure 3.2 The tractive,
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34 Gravity Mean sea level It might
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36 Gravity The benefits of space fl
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38 Gravity Figure 3.6 Profile of th
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40 Gravity Figure 3.8 The siphon at
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4 Optics Light is an electromagneti
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44 Optics Figure 4.2 Refraction. (a
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46 Optics The coeficient of reflect
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48 Optics only the light oscillatin
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50 Optics called Iceland Spar. Two
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52 Optics Diffraction If you shine
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54 Optics Figure 4.7 Geometrical op
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56 Optics Figure 4.9 The mirrors in
Page 75 and 76: 5 Atomic structure and age-dating P
Page 77 and 78: 60 Atomic structure and age-dating
Page 83 and 84: 66 Electromagnetic radiation radiat
Page 85 and 86: 68 Electromagnetic radiation Source
Page 87 and 88: Heat and heat flow The noun heat ha
Page 89 and 90: 72 Heat and heat flow Second Law: A
Page 91 and 92: 8 Electricity and magnetism Electri
Page 93 and 94: Electricity and magnetism 77 Figure
Page 95 and 96: Electricity and magnetism 79 rivett
Page 97 and 98: Electricity and magnetism 8 1 defin
Page 99 and 100: Electricity and magnetism 83 is kno
Page 101 and 102: 9 Stress and strain Pressure, p, is
Page 103 and 104: Stress and strain 87 than some natu
Page 105 and 106: These three elastic constants are r
Page 107 and 108: Stress and strain 91 Figure 9.1 New
Page 109 and 110: Stress and strain 93 Figure 9.2 Com
Page 111 and 112: Stress and strain 95 Figure 9.3 Ide
Page 113 and 114: Fracture Stress and strain 97 We fo
Page 115 and 116: Stress and strain 99 from which we
Page 117 and 118: 10 Sea waves The nature of water wa
Page 119 and 120: Sea waves 103 Figure 10.1 Wave moti
Page 121 and 122: Sea waves 105 refraction by islands
Page 123 and 124: Acoustics: sound and other waves 10
Page 125: Acoustics: sound and other waves 10
Page 129 and 130: Fluids and fluid flow 1 13 Figure 1
Page 131 and 132: Fluids and fluid flow 115 Figure 22
Page 133 and 134: Fluids and fluid flow 117 and the f
Page 135 and 136: water above a vertical thickness h
Page 137 and 138: Fluids and fluid flow 121 where V i
Page 139 and 140: Fluids and fluid flow 123 ardentes,
Page 141 and 142: Fluids and fluid flow 125 Figure 12
Page 143 and 144: - 14 $ 12 E 10 K .- 3 8 r cll + 6 0
Page 145 and 146: Fluids and fluid flow 129 the liqui
Page 147 and 148: Some dangers of mathematical statis
Page 155 and 156: Appendix 139 What would happen if y
Page 157 and 158: Notes 141 and since x is very large
Page 159 and 160: References Allum, J. A. E. (1966) P
Page 161 and 162: References 145 -(1950) 'Mechanism o
Page 163: Further reading 147 Trigg, G. L. an
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Physics for Geologists, Second edition

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