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The Physics Teacher

American Journal of Physics»
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Letters To The Editor
Editorial
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Volume 47

Issue 12 | Dec 1979 | pp. 1017-1111

Issue 11 | Nov 1979 | pp. 925-1016

Issue 10 | Oct 1979 | pp. 833-924

Issue 9 | Sep 1979 | pp. 757-832

Issue 8 | Aug 1979 | pp. 665-755

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Jul 1979

Volume 47, Issue 7, pp. 573-663

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Letters To The Editor

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Regarding: Editorial: Where are the problems?

Hugh Nutley

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 573

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Abstract Unavailable

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01.40.-d

Education

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On the de Broglie wavelength of 10−ton Kenworth trucks

A.C. Tanner

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 573

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Abstract Unavailable

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01.55.+b	General physics
03.65.-w	Quantum mechanics

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A response to ’’Dilemma of the primary colors’’

Marvin Hoshino

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 573 | Cited 1 time

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Abstract Unavailable

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07.68.+m	Photography, photographic instruments; xerography
42.66.-p	Physiological optics

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The weight‐mass controversy

Hugh C. Wolfe

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 574

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Abstract Unavailable

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06.20.F-

Units and standards

Editorial

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Editorial: From yardsticks to metersticks.II

John S. Rigden

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 575

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Abstract Unavailable

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01.40.-d

Education

Papers

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What you see is what you get!

David Harrison

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 576

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The issue of observability and the relative roles of the senses and reason in understanding the world is reviewed. Eastern ’’mystical’’ philosophy is used as a focus in which interpretations of quantum mechanics, as well as the current bootstrap‐quark controversy, can be seen in some slightly different contexts than usual.

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01.70.+w	Philosophy of science
01.65.+g	History of science
01.55.+b	General physics
03.65.-w	Quantum mechanics

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Do springboard divers violate angular momentum conservation?

Cliff Frohlich

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 583 | Cited 10 times

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No. However, divers and trampolinists can perform somersaults and twists even though they have zero angular momentum at all times during the stunt. Also, if a diver is somersaulting in space and possesses angular momentum only about his somersaulting axis, he can make a single discrete change in the position of his arms which initiates continuous twisting motion even in the absence of any applied torque. These apparent paradoxes have confused both physicists and coaches for some time. The present paper attempts to reduce this confusion. It discusses several different methods that performers use to initiate somersaults and twists and presents concrete examples of each method. Wherever possible quantitative calculations are presented and evaluated using information about the moments of inertia, mass, etc., of ’’typical’’ performers.

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01.55.+b	General physics
45.05.+x	General theory of classical mechanics of discrete systems
87.19.-j	Properties of higher organisms

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Simple C_p/C_v resonance apparatus suitable for the physics teaching laboratory

D. G. Smith

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 593 | Cited 6 times

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A resonance apparatus for the measurement of C_p/C_v for different gases is described. In the apparatus a magnetically supported piston in a vertical cylindrical glass tube containing the gas is forced into oscillation by means of a standard audio signal generator. The apparatus is simple and inexpensive, and may be used for general work on forced oscillations and resonance.

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01.50.Pa	Laboratory experiments and apparatus
05.70.-a	Thermodynamics

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How monochromatic is laser light?

Stephen F. Jacobs

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 597 | Cited 4 times

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See Also: Erratum

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Two derivations of the fundamental laser linewidth are presented that have been used successfully in introductory courses. The cause of the finite linewidth is identified with phase fluctuations in the electric field due to spontaneous emission. A factor of 2 discrepancy between the energy and field analyses is explained. A number of ’’back‐of‐the‐envelope’’ relationships are derived that have proven useful in teaching this subject.

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42.60.-v	Laser optical systems: design and operation
42.55.-f	Lasers
02.30.-f	Function theory, analysis

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Relativistic transformations of light power

John M. McKinley

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 602 | Cited 5 times

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Using a photon‐counting technique, we find the angular distribution of emitted and detected power and the total radiated power of an arbitrary moving source. We compare these expressions to the incorrect or incomplete expressions previously reported. We use the technique to verify the predicted effect of the earth’s motion through the cosmic blackbody radiation.

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03.30.+p

Special relativity

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New mathematical proof of the uncertainty relation

David N. Williams

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 606 | Cited 2 times

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We present a new proof of the uncertainty relation for wave functions that are absolutely integrable and have absolutely integrable Fourier transforms.

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03.65.Ta	Foundations of quantum mechanics; measurement theory
02.30.-f	Function theory, analysis

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Cardiovascular simulator for the undergraduate physics laboratory

L. J. Bruner

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 608

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An apparatus for simulation of blood flow through the heart and systemic circulation has been constructed. Catheter coupling to an externally mounted strain gauge transducer permits dynamic measurement of arterial and venous pressures. With the simulator, students can observe the effects of stroke volume and rate upon maximum, minimum, and mean arterial pressure. Additional demonstrations are discussed.

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01.50.My	Demonstration experiments and apparatus
87.19.-j	Properties of higher organisms
07.10.-h	Mechanical instruments and equipment

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Analog computer laboratory with biological examples

Donald E. Strebel

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 612 | Cited 1 time

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The use of biological examples in teaching applications of the analog computer is discussed. In an introductory general physics laboratory class which included biology majors, the addition of some biologically relevant analog computer problems was well received. The response indicates that such problems can be particularly useful in physics classes which include life‐science students or which explore biophysics topics. Several suitable examples from mathematical ecology, enzyme kinetics, and tracer dynamics are described.

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01.50.ht	Instructional computer use
87.10.-e	General theory and mathematical aspects
89.60.-k	Environmental studies

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Simple astronomical theory of climate

Reuben Benumof

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 619

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By applying perturbation theory to a highly simplified solar system, we find that the semimajor axis of the Earth’s orbit is secularly invariant, the square of the eccentricity varies approximately sinusoidally with a secular period of 93 000 years, and the perihelion precesses toward the northern summer solstice with a period of approximately 21 000 years relative to the moving vernal equinox. The Earth’s axis also nutates with a period of 41 000 years. These periods correlate very well with the periods found in the climatic record. The secular periods of the Earth’s orbital parameters determine the variation with time of the average intensity of solar radiation and thus may trigger the onset of ice ages.

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92.60.Ry	Climatology, climate change and variability
91.10.-v	Geodesy and gravity
96.60.Tf	Solar electromagnetic emission

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Lagrangians and systems they describe—how not to treat dissipation in quantum mechanics

John R. Ray

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 626 | Cited 22 times

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A Lagrangian that yields equations of motion for a damped simple harmonic oscillator is shown not to describe this system, but a completely different physical system. Thus, we have a simple counterexample to the statement: ’’If a Lagrangian gives the correct equations of motion for a given system then the Lagrangian describes the system.’’ We also construct a physical system that the Lagrangian describes and derive some of its properties. The quantum theory based on the above Lagrangian has been used to attempt to discuss the quantum theory of dissipation. This is, however, incorrect since the system the Lagrangian describes has no dissipation.

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45.05.+x	General theory of classical mechanics of discrete systems
03.65.-w	Quantum mechanics

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Pseudopotentials for excited states of hydrogen: A vivid illustration of limitations to the use of pseudopotential results

P. L. Goodfriend

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 630

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It is shown that exact pseudopotentials for excited states of hydrogen atoms can be derived. Use is made of this novel application of pseudopotential theory to display limitations to the use of pseudopotential results.

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03.65.Ge	Solutions of wave equations: bound states
31.15.-p	Calculations and mathematical techniques in atomic and molecular physics

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An inexpensive torsional pendulum apparatus for rigidity modulus measurement

S. Tyagi and A. E. Lord, Jr.

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 632

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We describe an easy to assemble torsional pendulum which can be put together for about $5 from parts available at any hardware store. The accuracy obtained in the measurement of the modulus of rigidity, G, is comparable the accuaracy obtained with the more expensive commercially available student models.

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01.50.Pa	Laboratory experiments and apparatus
01.55.+b	General physics
07.10.-h	Mechanical instruments and equipment

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Limiting spectra from confining potentials

Michael Martin Nieto and L. M. Simmons, Jr.

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 634 | Cited 5 times

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For confining potentials and large quantum numbers, the bound‐state energies rise more rapidly as a function of n the more rapidly the potential rises with distance. However, the spectrum can rise no faster than n² in the nonrelativistic case, or n in the relativistic case.

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03.65.-w	Quantum mechanics
13.90.+i	Other topics in specific reactions and phenomenology of elementary particles (restricted to new topics in section 13)
14.80.-j	Other particles (including hypothetical)

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Application of Hamilton’s principle to the study of the anharmonic oscillator in classical mechanics

Harvey Gilmartin, Abraham Klein, and Ching‐teh Li

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 636 | Cited 1 time

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A form of Hamilton’s principle for classical mechanics, appropriate to the study of arbitrary self‐sustained vibrations in one dimension is presented. It is applied as an approximate computational tool to the study of several examples of anharmonic oscillation. The trial function is a finite Fourier series chosen to approach the exact solution as the number of terms increases without limit. Analytic approximations can be obtained for the limits of weak and strong anharmonicity. Numerical results for the amplitude‐dependent frequencies compare favorably with the exact solutions.

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45.05.+x	General theory of classical mechanics of discrete systems
01.55.+b	General physics
02.60.-x	Numerical approximation and analysis

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Small amplitude oscillations of a quasi‐ideal pendulum

R. J. Gleiser

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 640

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A variational principle, resembling that used in quantum mechanics, is formulated and applied to study the first‐order correction to the period of a simple pendulum. The relevant small parameter is the ratio of the mass of the suspension cord to that of the pendulum bob. The suspension cord is assumed inextensible but otherwise both its elastic properties and mass distribution are arbitrary. Results previously derived independently for a rigid rod or flexible cord suspension are thus obtained within a single formalism. The discussion of the connection between these cases and of related results is thereby simplified.

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45.05.+x

General theory of classical mechanics of discrete systems

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The Schrödinger‐Einstein correspondence and the sources of wave mechanics

Paul A. Hanle

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 644 | Cited 1 time

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Unpublished letters of late 1925 between Einstein and Schrödinger and the doctoral thesis of de Broglie reveal sources of Schrödinger’s inspiration to invent wave mechanics. Schrödinger saw a congenial similarity of de Broglie’s work on the stability of the atom with his own earlier speculation in relativity, which he noted to Einstein. But the last chapter of de Broglie’s thesis, on quantum statistics of gases, which is unfamiliar to many modern readers, provided Schrödinger with the method of treatment of a gas of material particles considered as a system of modes of vibration, of ’’matter waves.’’ This method especially, and other successes of de Broglie’s ’’ingenious thesis,’’ convinced Schrödinger to take seriously the first part, on the conditions of stability of the atom in a wave picture. Thus he sought and found an equation to describe the states of the electron from the matter‐wave viewpoint.

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01.65.+g	History of science
03.65.-w	Quantum mechanics

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Concise derivation of the rotational partition function

F. Hynne and Knud Andersen

American Journal of Physics -- July 1979 -- Volume 47, Issue 7, pp. 649

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The classical partition function for the rotation of a rigid asymmetric molecule is derived by a transformation of variables in the phase integral circumventing the cumbersome manipulations of the canonical prescription.

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05.20.-y

Classical statistical mechanics