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Dec 1955

Volume 23, Issue 9, pp. 557-626

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Forced Vibration with Damping

D. A. Richards

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 557

Online Publication Date: Jul 2005

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The experimental determination of the response curves for forced vibration with velocity damping, using a moving-coil galvanometer, is described. The mechanism for producing a sinusoidal emf, of continuously variable frequency ranging from zero to 0.4 cy/sec, is described, together with a method for the determination of the phase angle between the driving force and the motion of the driven system. Experimental results, obtained with the apparatus, both for response curves and phase angle measurements, for various values of damping, are summarized in the paper.

Vibrational Dynamics with Lenses, Mirrors, and Prisms

John Satterly

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 562

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In previous papers I have described experiments on the rocking of bodies. The rocking bodies have bearing surfaces which are plane, circular, or elliptical and they may rock on circular, elliptical, or plane surfaces.
Lenses also furnish interesting examples of rocking bodies. Their surfaces may be spherical, cylindrical, or plane and these have the advantage that they are smooth and of good geometrical form. Their curvatures may be measured accurately with calipers and spherometer. To lenses may be added prisms and mirrors. Odd lenses, prisms, and mirrors usually abound in a well-stocked laboratory so that examples are not far to seek. The larger the specimens the more easily do they lend themselves to experimentation. The calculations of the period of rocking furnish, as in earlier papers, interesting examples of the applications of mechanics to vibrational problems, and the calculation of positions of centers of gravity and values of moments of inertia provide additional exercises. The experiments are eminently suitable for senior classes in the physical laboratory, giving interest to the student by their novelty and little trouble to the demonstrators in the matter of putting out the apparatus for the use of the class. Their number illustrates the variations possible with very little apparatus.

On Deriving the Formulas for Electromagnetic and Other Forces from the Interaction Energy of the Fields

H. L. Armstrong

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 582

Online Publication Date: Jul 2005

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A treatment of some force and energy relations of electromagnetic theory is given, in which the energy density of the field is postulated as fundamental, and the force relations are derived by transformations of vector integrals. This focuses attention on the fields as the concepts of especial interest; the attention to interaction energies of fields offers interesting analogies to the methods used in wave mechanics.

Spin Resonance Line Shape

Jerome I. Kaplan

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 585

Online Publication Date: Jul 2005

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A method is given for the calculation of the spin resonance equations based on solving for the spin vector expectation value subject to several external conditions. The value of the method is limited to the case where the system can be described by one relaxation time.

Note on the Derivation of the Equation v = math

Henry S. C. Chen

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 588

Online Publication Date: Jul 2005

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A simple, straightforward derivation is given for the speed of a transverse wave along a stretched string. It is free from the many limitations and assumptions which are generally found in other derivations. The only assumption which has to be made here is that the wave travels with a constant speed and small amplitude.

Hydromagnetism. I. A Review

Walter M. Elsasser

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 590

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This paper gives a survey of the theories (Part I) and phenomena (Part II) of cosmic magnetism, extending from geomagnetism over solar and sunspot magnetism to stellar and interstellar magnetic fields. The theoretical treatment is purely classical and Maxwelliam. Most cosmic fluids, being highly ionized, are excellent conductors; this implies that the displacement current can always be neglected. The fundamental equations of hydromagnetism are the electromagnetic field equations together with the hydrodynamic equation, both containing coupling terms between magnetic field and motion. Among other theoretical developments, the “dynamo” theory which ascribes the cosmic magnetic fields to amplifying processes in the moving fluid is described and it is shown that it is well suited to represent the observed phenomena of the generation and maintenance of cosmic magnetic fields.

Practical Aids for Physics Teachers

L. R. Ingersoll

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 609

Online Publication Date: Jul 2005

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Abstract Unavailable

Physics in Engineering

W. V. Houston

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 610

Online Publication Date: Jul 2005

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The application of discoveries made in pure science to engineering problems is described and illustrated by incidents in the history of submarine telegraph cables, radio communication, and electronics.

Heat Units and Temperature Scales for Calorimetry

H. F. Stimson

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 614 | Cited 5 times

Online Publication Date: Jul 2005

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Calorimetry is the measurement of quantities of heat. Temperature scales are usually involved. The General Conference on Weights and Measures adopted the International Temperature Scale (practical scale) in 1927 and its first revision in 1948. This scale is nearly parallel to the thermodynamic scale, proposed by Kelvin in 1854. In 1954 the General Conference redefined the Kelvin Scale, in the manner which Kelvin originally said “must be adopted ultimately,” by assigning a value for the temperature of a single fixed point, viz. 273.16° for the triple point of water (ice point=273.15°). Several calories have been used in the past but the joule was adopted for the unit of quantity of heat in 1948. The need is stressed for using units of heat which are unambiguous.
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Concerning Index of Refraction and Density

E. Scott Barr

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 623 | Cited 1 time

Online Publication Date: Jul 2005

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Concerning the Complex Conjugate of a Function

S. Y. Tiwari and B. Bhattacharya

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 624

Online Publication Date: Jul 2005

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A Mechanics Demonstration

Paul O. Hoffmann

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 624

Online Publication Date: Jul 2005

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Abstract Unavailable
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Physics—A Descriptive Interpretation

Charles H. Bachman, Author and John J. Heilemann, Reviewer

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 625

Online Publication Date: Jul 2005

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Household Physics

Madalyn Avery, Author and Lester T. Earls, Reviewer

American Journal of Physics -- December 1955 -- Volume 23, Issue 9, pp. 626

Online Publication Date: Jul 2005

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