sn/ch99/glossary.tex

   1 \refstepcounter{appendixctr}\label{glossaryappendix}%
   2 \appendix\chapter{Appendix \ref{glossaryappendix}: Glossary}
   3
   4 \textbf{Absorption}. What happens when wave passes through a medium and gives up some of its energy.
   5
   6 \textbf{Acceleration}. The rate of change of velocity, $\der{}v/\der{}t$.
   7
   8 \textbf{Alpha decay}. The radioactive decay of a nucleus via emission of an alpha particle.
   9
  10
  11 \textbf{Alpha particle}. A form of radioactivity consisting of helium nuclei.
  12
  13 \textbf{Ammeter}. A device for measurin electrical current.
  14
  15 \textbf{Ampere}. The metric unit of current, one coulomb per second; also ``amp."
  16
  17
  18 \textbf{Amplitude}. The amount of vibration, often measured from the center to one side; may have different
  19 units
  20 depending on the nature of the vibration.
  21
  22 \textbf{Angular magnification}. The factor by which an image's apparent angular size is increased (or
  23 decreased). Cf. magnification.
  24
  25 \textbf{Angular momentum}. A measure of rotational motion; a conserved quantity for a closed system.
  26
  27 \textbf{Atom}. The basic unit of one of the chemical elements.
  28
  29 \textbf{Atomic mass}. The mass of an atom.
  30
  31 \textbf{Atomic number}. The number of protons in an atom's nucleus; determines what element it is.
  32
  33 \textbf{Attractive}. Describes a force that tends to pull the two participating objects together. Cf.
  34 repulsive, oblique.
  35
  36
  37 \textbf{Axis}. An arbitrarily chosen point used in the definition of angular momentum. Any object whose
  38 direction changes
  39 relative to the axis is considered to have angular momentum. No matter what axis is chosen, the angular
  40 momentum of a
  41 closed system is conserved.
  42
  43 \textbf{Beta decay}. The radioactive decay of a nucleus via the reaction \mbox{n $\to$ p + e$^{-}$ + $\overline \nu $} or\\
  44 \mbox{p $\to$ n + e$^{+}$ + $\nu$}; so
  45 called because an electron or antielectron is also known as a beta particle.
  46
  47 \textbf{Beta particle}. A form of radioactivity consisting of electrons.
  48
  49 \textbf{Cathode ray}. The mysterious ray that emanated from the cathode in a vacuum tube; shown by Thomson to
  50 be a stream of particles smaller than atoms.
  51
  52 \textbf{Center of mass}. The balance point of an object.
  53
  54 \textbf{Charge}. A numerical rating of how strongly an object participates in electrical forces.
  55
  56 \textbf{Circuit}. An electrical device in which charge can come back to its starting point and be recycled
  57 rather than getting stuck in a dead end.
  58
  59 \textbf{Coherent}. A light wave whose parts are all in phase with each other.
  60
  61 \textbf{Collision.}     An interaction between moving objects that lasts for a certain time.
  62
  63 \textbf{Component}. The part of a velocity, acceleration, or force that is along one particular coordinate
  64 axis.
  65
  66 \textbf{Concave}. Describes a surface that is hollowed out like a cave.
  67
  68 \textbf{Convex}. Describes a surface that bulges outward.
  69
  70 \textbf{Coulomb (C)}. The unit of electrical charge.
  71
  72 \textbf{Current}. The rate at which charge crosses a certain boundary, $\der{}q/\der{}t$.
  73
  74 \textbf{Damping}. the dissipation of a vibration's energy into heat energy, or the frictional force that
  75 causes the loss
  76 of energy.
  77
  78 \textbf{Diffraction}. The behavior of a wave when it encounters an obstacle or a nonuniformity in its medium;
  79 in general, diffraction causes a wave to bend around obstacles and make patterns of strong and weak waves
  80 radiating out beyond the obstacle.
  81
  82 \textbf{Diffuse reflection}. Reflection from a rough surface, in which a single ray of light is divided up
  83 into many weaker reflected rays going in many directions.
  84
  85 \textbf{Displacement}. (avoided in this book) A name for the symbol $\Delta{}x$.
  86
  87 \textbf{Driving force}. An external force that pumps energy into a vibrating system.
  88
  89 \textbf{Electric dipole}. An object that has an imbalance between positive charge on one side and negative
  90 charge on the other; an object that will experience a torque in an electric field.
  91
  92 \textbf{Electric field}. The force per unit charge exerted on a test charge at a given point in space.
  93
  94 \textbf{Electrical force}. One of the fundamental forces of nature; a noncontact force that can be either
  95 repulsive or attractive.
  96
  97 \textbf{Electron}. Thomson's name for the particles of which a cathode ray was made; a subatomic particle.
  98
  99 \textbf{Energy}. A numerical scale used to measure the heat, motion, or other properties that would require
 100 fuel or
 101 physical effort to put into an object; a scalar quantity with units of joules (J).
 102
 103 \textbf{Equilibrium}. A state in which an object's momentum and angular momentum are constant.
 104
 105 \textbf{Field}. A property of a point in space describing the forces that would be exerted on a particle if it
 106 was there.
 107
 108 \textbf{Fission}. The radioactive decay of a nucleus by splitting into two parts.
 109
 110 \textbf{Fluid}. A gas or a liquid.
 111
 112 \textbf{Fluid friction}. A friction force in which at least one of the object is is a fluid (i.e. either a gas
 113 or a
 114 liquid).
 115
 116 \textbf{Focal length}. A property of a lens or mirror, equal to the distance from the lens or mirror to the
 117 image it forms of an object that is infinitely far away.
 118
 119 \textbf{Force}. The rate of transfer of momentum, $\der{}\myvec{p}/\der{}t$.
 120
 121 \textbf{Frequency}. The number of cycles per second, the inverse of the period (q.v.).
 122
 123 \textbf{Fusion}. A nuclear reaction in which two nuclei stick together to form one bigger nucleus.
 124
 125 \textbf{Gamma ray}. A form of radioactivity consisting of a very high-frequency form of light.
 126
 127 \textbf{Gravitational field}. The energy per unit mass and per unit distance required to list a mass, due
 128 to the attraction of other masses such as the planet earth.
 129
 130 \textbf{Gravity}. A general term for the phenomenon of attraction between things having mass. The attraction
 131 between our
 132 planet and a human-sized object causes the object to fall.
 133
 134 \textbf{Half-life}. The amount of time that a radioactive atom has a probability of 1/2 of surviving without
 135 decaying.
 136
 137 \textbf{Heat}. The energy that an object has because of its temperature. Heat is different from temperature
 138 (q.v.) because
 139 an object with twice as much mass requires twice as much heat to increase its temperature by the same
 140 amount. There is a
 141 further distinction in the terminology, not emphasized in this book, between heat and thermal energy. See
 142 the entry
 143 under thermal energy for a discussion of this distinction.
 144
 145 \textbf{Image}. A place where an object appears to be, because the rays diffusely reflected from any given
 146 point on the object have been bent so that they come back together and then spread out again from the image
 147 point, or spread apart as if they had originated from the image.
 148
 149 \textbf{Index of refraction}. An optical property of matter; the speed of light in a vacuum divided by the
 150 speed of light in the substance in question.
 151
 152 \textbf{Independence}. The lack of any relationship between two random events.
 153
 154 \textbf{Induction}. The production of an electric field by a changing magnetic field, or vice-versa.
 155
 156 \textbf{Inertial frame}. A frame of reference that is not accelerating, one in objects are only observed
 157 to change their state of motion due to interactions with other objects.
 158
 159
 160 \textbf{Invariant}. A quantity that does not change when transformed.
 161
 162 \textbf{Ion}. An electrically charged atom or molecule.
 163
 164 \textbf{Isotope}. One of the possible varieties of atoms of a given element, having a certain number of
 165 neutrons.
 166
 167 \textbf{Kinetic energy}. The energy an object has because of its motion. In nonrelativistic
 168 physics $K=(1/2)mv^2$.
 169
 170 \textbf{Kinetic friction}. A friction force between surfaces that are slipping past each other.
 171
 172 \textbf{Light}. Anything that can travel from one place to another through empty space and can influence
 173 matter, but is
 174 not affected by gravity.
 175
 176 \textbf{Lorentz transformation}. The transformation between frames in relative motion.
 177
 178 \textbf{Magnetic dipole}. An object, such as a current loop, an atom, or a bar magnet, that experiences
 179 torques due to magnetic forces; the strength of magnetic dipoles is measured by comparison with a standard
 180 dipole consisting of a square loop of wire of a given size and carrying a given amount of current.
 181
 182 \textbf{Magnetic field}. A field of force, defined in terms of the torque exerted on a test dipole.
 183
 184 \textbf{Magnification}. The factor by which an image's linear size is increased (or decreased). Cf. angular
 185 magnification.
 186
 187 \textbf{Magnitude}. The ``amount'' associated with a vector; the vector stripped of any information about its
 188 direction.
 189
 190 \textbf{Mass}. A numerical measure of how difficult it is to change an object's motion. (In the context of
 191 relativity, some books use the word``mass'' to mean what we refer to as mass multiplied by gamma.)
 192
 193 \textbf{Mass number}. The number of protons plus the number of neutrons in a nucleus; approximately
 194 proportional to its atomic mass.
 195
 196 \textbf{Matter}. Anything that is affected by gravity, or, more accurately, any particle whose spin is
 197 an odd multiple of $\hbar/2$.
 198
 199 \textbf{Millirem}. A unit for measuring a person's exposure to radioactivity; cf rem.
 200
 201 \textbf{Mks system}. The use of metric units based on the meter, kilogram, and second. Example: meters per
 202 second is the
 203 mks unit of speed, not cm/s or km/hr.
 204
 205 \textbf{Molecule}. A group of atoms stuck together.
 206
 207 \textbf{Momentum}. A measure of motion, equal to mv for material objects.
 208
 209 \textbf{Neutron}. An uncharged particle, the other types that nuclei are made of.
 210
 211 \textbf{Noninertial frame}. An accelerating frame of reference, in which Newton's first law is violated.
 212
 213 \textbf{Nonuniform circular motion}. Circular motion in which the magnitude of the velocity vector changes.
 214
 215 \textbf{Normal force}. The force that keeps two objects from occupying the same space.
 216
 217 \textbf{Normalization}. The property of probabilities that the sum of the probabilities of all possible
 218 outcomes must equal one.
 219
 220 \textbf{Oblique}. Describes a force that acts at some other angle, one that is not a direct repulsion or
 221 attraction. Cf.
 222 attractive, repulsive.
 223
 224 \textbf{Ohm}. The metric unit of electrical resistance, one volt per ampere.
 225
 226 \textbf{Ohmic}. Describes a substance in which the flow of current between two points is proportional to the
 227 voltage difference between them.
 228
 229 \textbf{Open circuit}. A circuit that does not function because it has a gap in it.
 230
 231 \textbf{Operational definition}. A definition that states what operations should be carried out to measure the
 232 thing being
 233 defined.
 234
 235 \textbf{Parabola}. The mathematical curve whose graph has $y$ proportional to $x^2$.
 236
 237 \textbf{Period}. The time required for one cycle of a periodic motion (q.v.).
 238
 239 \textbf{Periodic motion}. Motion that repeats itself over and over.
 240
 241 \textbf{Photon}. A particle of light.
 242
 243 \textbf{Photoelectric effect}. The ejection, by a photon, of an electron from the surface of an object.
 244
 245 \textbf{Potential energy}. The energy having to do with the distance between to objects that interact, or,
 246 in general, the energy stored in a field. Cf. Kinetic energy.
 247
 248 \textbf{Power}. The rate of transferring energy, $\der{}E/\der{}t$; a scalar quantity with units of watts (W).
 249
 250 \textbf{Probability}. The likelihood that something will happen, expressed as a number between zero and one.
 251
 252 \textbf{Probability distribution}. A curve that specifies the probabilities of various random values of a
 253 variable; areas under the curve correspond to probabilities.
 254
 255 \textbf{Proton}. A positively charged particle, one of the types that nuclei are made of.
 256
 257 \textbf{Quality factor}. The number of oscillations required for a system's energy to fall off by a factor of
 258 535 due to
 259 damping.
 260
 261 \textbf{Quantized}. Describes quantity such as money or electrical charge, that can only exist in certain
 262 amounts.
 263
 264 \textbf{Quantum number}. A numerical label used to classify a quantum state.
 265
 266 \textbf{Radial}. Parallel to the radius of a circle; the in-out direction. Cf. tangential.
 267
 268 \textbf{Real image}. A place where an object appears to be, because the rays diffusely reflected from any
 269 given point on the object have been bent so that they come back together and then spread out again from the
 270 new point. Cf. virtual image.
 271
 272 \textbf{Reflection}. What happens when light hits matter and bounces off, retaining at least some of its
 273 energy.
 274
 275 \textbf{Refraction}. The change in direction that occurs when a wave encounters the interface between two
 276 media.
 277
 278 \textbf{Rem}.  A unit for measuring a person's exposure to radioactivity; cf millirem.
 279
 280 \textbf{Repulsive}. Describes a force that tends to push the two participating objects apart. Cf. attractive,
 281 oblique.
 282
 283 \textbf{Resistance}. The ratio of the voltage difference to the current in an object made of an ohmic
 284 substance.
 285
 286 \textbf{Resonance}. The tendency of a vibrating system to respond most strongly to a driving force whose
 287 frequency is
 288 close to its own natural frequency of vibration.
 289
 290 \textbf{Rest mass}. Referred to as mass in this book; written as $m_0$ in some books. Cf. mass.
 291
 292 \textbf{Scalar}. A quantity that has no direction in space, only an amount. Cf. vector.
 293
 294 \textbf{Short circuit}. A circuit that does not function because charge is given a low-resistance``shortcut"
 295 path that it can follow, instead of the path that makes it do something useful.
 296
 297 \textbf{Significant figures}. Digits that contribute to the accuracy of a measurement.
 298
 299 \textbf{Simple harmonic motion}. Motion whose $x-t$ graph is a sine wave.
 300
 301 \textbf{Sink}. A point at which field vectors converge.
 302
 303 \textbf{Source}. A point from which field vectors diverge; often used more inclusively to refer to points of
 304 either convergence or divergence.
 305
 306 \textbf{Specular reflection}. Reflection from a smooth surface, in which the light ray leaves at the same
 307 angle at which it came in.
 308
 309 \textbf{Speed}. (avoided in this book) The absolute value of or, in more then one dimension, the magnitude of
 310 the
 311 velocity, i.e. the velocity stripped of any information about its direction
 312
 313 \textbf{Spring constant}. The constant of proportionality between force and elongation of a spring or other
 314 object under
 315 strain.
 316
 317 \textbf{Spin}. The built-in angular momentum possessed by a particle even when at rest.
 318
 319 \textbf{Stable equilibrium}. One in which a force always acts to bring the object back to a certain point.
 320
 321 \textbf{Static friction}. A friction force between surfaces that are not slipping past each other.
 322
 323 \textbf{Steady state}. The behavior of a vibrating system after it has had plenty of time to settle into a
 324 steady response
 325 to a driving force. In the steady state, the same amount of energy is pumped into the system during each
 326 cycle as is
 327 lost to damping during the same period.
 328
 329 \textbf{Strong nuclear force}. The force that holds nuclei together against electrical repulsion.
 330
 331 \textbf{Systeme International.} Fancy name for the metric system.
 332
 333 \textbf{Tangential}. Tangent to a curve. In circular motion, used to mean tangent to the circle, perpendicular
 334 to the
 335 radial direction Cf. radial.
 336
 337 \textbf{Temperature}. What a thermometer measures. Objects left in contact with each other tend to reach the
 338 same
 339 temperature. Roughly speaking, temperature measures the average kinetic energy per molecule. For the
 340 distinction between
 341 temperature and heat, see the glossary entry for heat.
 342
 343 \textbf{Thermal energy}. Careful writers make a distinction between heat and thermal energy, but the
 344 distinction is often
 345 ignored in casual speech, even among physicists. Properly, thermal energy is used to mean the total amount
 346 of energy
 347 possessed by an object, while heat indicates the amount of thermal energy transferred in or out. The term
 348 heat is used in
 349 this book to include both meanings.
 350
 351 \textbf{Torque}. The rate of change of angular momentum, $\der{}L/\der{}t$; a numerical measure of a force's ability to twist on
 352 an object.
 353
 354
 355 \textbf{Transformation}. The mathematical relationship between the variables such as $x$ and $t$, as observed in
 356 different frames of reference.
 357
 358 \textbf{Uniform circular motion}. Circular motion in which the magnitude of the velocity vector remains
 359 constant.
 360
 361
 362 \textbf{Vector}. A quantity that has both an amount (magnitude) and a direction in space. Cf. scalar.
 363
 364 \textbf{Unstable equilibrium.} One in which any deviation of the object from its equilibrium position results
 365 in a force
 366 pushing it even farther away.
 367
 368 \textbf{Velocity}. The rate of change of position, $\der{}x/\der{}t$.
 369
 370 \textbf{Virtual image}. Like a real image, but the rays don't actually cross again; they only appear to have
 371 come from the point on the image. Cf. real image.
 372
 373 \textbf{Volt}. The metric unit of voltage, one joule per coulomb.
 374
 375 \textbf{Voltage}. Electrical potential energy per unit charge that will be possessed by a charged particle at
 376 a certain point in space.
 377
 378 \textbf{Voltmeter}. A device for measuring voltage differences.
 379
 380 \textbf{Wave-particle duality}. The idea that light is both a wave and a particle.
 381
 382 \textbf{Wavefunction}. The numerical measure of an electron wave, or in general of the wave corresponding to
 383 any quantum mechanical particle.
 384
 385 \textbf{Weak nuclear force}. The force responsible for beta decay.
 386
 387 \textbf{Weight}. The force of gravity on an object, equal to $mg$.
 388
 389 \textbf{Work}. The amount of energy transferred into or out of a system, excluding energy transferred by heat
 390 conduction.
 391