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Dec 2001

Volume 69, Issue 12, pp. 1221-1287

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Broken telephone games in the history of science

Craig F. Bohren

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1221 | Cited 2 times

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Abstract Unavailable
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01.60.+q Biographies, tributes, personal notes, and obituaries
01.65.+g History of science
01.40.-d Education
01.50.-i Educational aids
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Quantitative experiments in electric and fluid flow field mapping

Richard A. Young

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1223 | Cited 3 times

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A system employing a voltage probe attached to an XY recorder is used to sample the electrical potential over a grid of points on conducting paper. Using commercial plotting software, the three-dimensional (3D) perspective of the potential (or equipotential contour lines) may then be displayed as a function of position. The charge density and the associated electric field are obtained by direct numerical differentiation of the potential data, and charge densities are displayed in a 3D perspective to reveal their spatial variation. Experimental results for screening and image charge densities on conductors are in excellent agreement with theoretical predictions obtained using conformal mapping methods. In addition, by exploiting the analogy between electric fields and fluid flow, the experimental system may also be used to model two-dimensional fluid dynamics. In this context, results for the velocity profile and the pressure distribution surrounding a wing moving through a fluid are presented. © 2001 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
47.40.-x Compressible flows; shock waves

Computer sound card assisted measurements of the acoustic Doppler effect for accelerated and unaccelerated sound sources

T. J. Bensky and S. E. Frey

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1231 | Cited 15 times

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An approach to experimentally measuring the speed of a moving object by direct application of the Doppler effect for sound is discussed. The method presented here uses a Windows computer and sound card to record Doppler shifted sound from a moving source. This sound card approach allows for direct acquisition of Doppler shifted sound intensity as a function of time, affording much analytical and pedagogical freedom in undergraduate lab instruction. In addition, the acquisition of such data allows for the experimental study of not only constant velocity sound sources, but of accelerated sound sources as well. © 2001 American Association of Physics Teachers.
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01.50.My Demonstration experiments and apparatus
01.50.Lc Laboratory computer use
06.30.Gv Velocity, acceleration, and rotation
43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers

The relation between physical and computer-generated point spread functions and optical transfer functions

Robert L. Lucke

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1237

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A review of how a point spread function and an optical transfer function are derived from the exit pupil function of an imaging system is given and the relation between computer-generated functions and their physical counterparts is developed in detail. Useful normalizations and integral relations are presented. © 2001 American Association of Physics Teachers.
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42.30.Lr Modulation and optical transfer functions
01.50.-i Educational aids
02.30.Rz Integral equations

Note on solving for the dynamics of the Universe

José Ademir Sales Lima

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1245 | Cited 2 times

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In a recent article, Faraoni proposed an alternative procedure to solve the Friedman–Lemaître–Robertson–Walker cosmological equations. The basic result of that paper was obtained long ago through a different approach, which seems to be little known and deserves closer attention due to its pedagogical interest. The broad importance of this method is readily recognized by examining some additional cases not considered by Faraoni. Its instructive potential for introductory courses on cosmology has been positively verified by the author in many lectures during the last decade. © 2001 American Association of Physics Teachers.
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98.80.Jk Mathematical and relativistic aspects of cosmology
98.80.Qc Quantum cosmology
04.40.-b Self-gravitating systems; continuous media and classical fields in curved spacetime
01.50.-i Educational aids
95.30.Sf Relativity and gravitation
04.20.Cv Fundamental problems and general formalism

Gyroscope precession and general relativity

Barry R. Holstein

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1248 | Cited 4 times

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Precession of a gyroscope in the presence of a gravitational field is of considerable interest, on account of the soon to be launched satellite test and because of its connection to Mach’s principle. Nevertheless, this topic is not generally covered in the curriculum because of the mathematical sophistication required. We examine some of the simple physics involved and argue that by examining simple graviton-elementary particle couplings one can easily understand this phenomenon. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
45.40.Cc Rigid body and gyroscope motion
04.20.Cv Fundamental problems and general formalism

On radar time and the twin “paradox”

Carl E. Dolby and Stephen F. Gull

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1257 | Cited 12 times

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In this paper we apply the concept of radar time (popularized by Bondi in his work on k calculus) to the well-known relativistic twin “paradox.” Radar time is used to define hypersurfaces of simultaneity for a class of traveling twins, from the “immediate turn-around” case, through the “gradual turn-around” case, to the “uniformly accelerating” case. We show that this definition of simultaneity is independent of choice of coordinates, and assigns a unique time to any event (with which the traveling twin can send and receive signals), resolving some common misconceptions. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
03.30.+p Special relativity

A tutorial presentation of the two stream instability and Landau damping

D. Anderson, R. Fedele, and M. Lisak

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1262 | Cited 4 times

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A tutorial presentation is given of the interaction between a high frequency electrostatic wave and a plasma. The analysis is carried out in several consecutive simple steps, starting from electrostatic plasma waves in a cold plasma and successively introducing complications like streaming electrons, the two stream instability and eventually the Landau damping phenomenon. The analysis is based only on cold plasma fluid theory and does not involve kinetic Vlasov theory. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Surface response of a conductor: static and dynamic, electric and magnetic

W. L. Schaich

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1267 | Cited 2 times

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The response of a flat metal surface to an external point charge or monopole moving parallel to it is analyzed for a variety of cases. The same basic formalism of matching partial wave expansions is used for each case with slight adaptations in order to emphasize the common physics as one determines the induced forces. The point disturbance is either stationary or moving at constant speed (and height) or suddenly appearing. The metal’s response is first treated via electrostatics and then generalized to electrodynamics. The influence of the metal’s thickness is studied in separate calculations wherein it ranges from semi-infinite down to much less than the penetration depth of the induced fields. The latter limit allows considerable analytic progress and an alternate description in terms of receding images.© 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Electric and magnetic forces and energies for a parallel-plate capacitor and a flattened, slip-joint solenoid

Timothy H. Boyer

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1277 | Cited 2 times

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A current-carrying solenoid can be imagined as fitted with slip-joints and flattened into a shape comparable to a parallel-plate capacitor. In this shape it is easy to calculate forces, the work done, and energy changes that are analogous to those for a capacitor with constant charge or constant voltage. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
84.32.Hh Inductors and coils; wiring
84.32.Tt Capacitors

Solving boundary-value electrostatics problems using Green’s reciprocity theorem

Ben Yu-Kuang Hu

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1280 | Cited 1 time

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Formal solutions to electrostatics boundary-value problems are derived using Green’s reciprocity theorem. This method provides a more transparent interpretation of the solutions than the standard Green’s function derivation. An energy-based argument for the reciprocity theorem is also presented. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
02.60.Lj Ordinary and partial differential equations; boundary value problems
02.60.Jh Numerical differentiation and integration
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Comment on “The van der Waals interaction,” by Barry R. Holstein [Am. J. Phys. 69 (4), 441–449 (2001)]

Barry R. Holstein

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1283

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Abstract Unavailable
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01.65.+g History of science
03.65.-w Quantum mechanics
34.20.Gj Intermolecular and atom-molecule potentials and forces

Comment on “Walking a charged pith ball perpendicular to an electric field,” by P. J. Ouseph and C. L. Davis [Am. J. Phys. 69 (1), 88–90 (2001)]

Paul J. Dolan, Jr.

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1283

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Two geometric arguments are presented that assist in visualizing the fact that a pith ball, between two almost parallel plates, will acquire a net motion in a direction perpendicular to the electric field. © 2001 American Association of Physics Teachers.
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01.50.-i Educational aids
41.20.-q Applied classical electromagnetism

Comment on “Troy Ounces (or Tons) of Silver,” by Dean S. Edmonds [Am. J. Phys. 69 (6), 629–630 (2001)]

Burt Brody

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1284

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Abstract Unavailable
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01.65.+g History of science
01.50.-i Educational aids
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Time and Chance

David Z. Albert, Author and Hans Christian von Baeyer, Reviewer

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1285

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Abstract Unavailable
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01.30.Vv Book reviews
01.50.-i Educational aids
05.70.-a Thermodynamics

Time for Science Education: How Teaching the History and Philosophy of Pendulum Motion Can Contribute to Science Literacy

Michael R. Matthews, Author and Mark A. Peterson, Reviewer

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1286

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Abstract Unavailable
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01.40.-d Education
01.65.+g History of science
01.70.+w Philosophy of science
01.30.Vv Book reviews
07.10.-h Mechanical instruments and equipment

CP Violation

I. I. Bigi, Author, A. I. Sanda, Author, and Bruce Winstein, Reviewer

American Journal of Physics -- December 2001 -- Volume 69, Issue 12, pp. 1287

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Abstract Unavailable
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01.30.Vv Book reviews
11.30.Er Charge conjugation, parity, time reversal, and other discrete symmetries
13.35.Dx Decays of taus
12.60.-i Models beyond the standard model
14.60.Fg Taus
12.15.-y Electroweak interactions
14.40.Nd Bottom mesons (|B|>0)
14.40.Be Light mesons (S=C=B=0)
13.20.Eb Decays of K mesons
14.60.Pq Neutrino mass and mixing
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