摘要:

Newton’s Second Law is equivalent to the continuity equation for momentum in integral form. This insight leads to an alternative picture of forces as momentum currents. The purpose of the present paper is to introduce a new approach to statics problems and their solutions in terms of momentum currents. In particular, the relation between the distribution of momentum currents and the elastic stresses within a medium will be considered and a simple way to pictorially represent those stresses with the help of momentum flow diagrams will be discussed. Handling statics problems in the momentum current picture immediately displays their relationship to analogous problems in electrical network theory. This uncovers a structural relationship between the role of electric charge in the theory of electricity and the role of momentum in mechanics. For example, it will be shown that the familiar method for the solution of statics problems in terms of free‐body diagrams is equivalent to the use of a junction rule for momentum currents.

ISSN:0002-9505    

DOI:10.1119/1.13923

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The distribution of light in the focal region of a lens in two dimensions is calculated in terms of the Fresnel integral. The result is a comparatively simple but very good analog for the focal region of a three‐dimensional lens discussed by Born and Wolf. In particular the cigar‐shaped channel through which the light penetrates the focal plane appears in the two‐dimensional as well as the three‐dimensional case.

ISSN:0002-9505    

DOI:10.1119/1.13924

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

It is shown that most initial states, upon sudden expansion of the wall of an infinite square well, lead to an infinite dispersion in the energy. Circumstances under which ΔEremains finite and constant are discussed. The situation with respect to a macroscopic system is examined.

ISSN:0002-9505    

DOI:10.1119/1.13727

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The Weeks–Chandler–Anderson perturbation theory is derived for one‐dimensional Lennard–Jones systems. Its predictions are tested with molecular dynamics calculations on the full and repulsive Lennard–Jones potential. It is found that the prescription for the reference fluid is in excellent agreement with the computer calculations and that the high‐temperature approximation for the full Lennard–Jones system is a good one at high temperatures.

ISSN:0002-9505    

DOI:10.1119/1.13728

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The Schlögl model of a nonlinear chemical reaction with diffusion is presented as an example of a reaction‐diffusion system displaying a nonequilibrium phase transition. It is described by a scalar diffusion equation with a cubic nonlinearity and is used here to show such features of nonlinear systems as bifurcations and spatial dissipative structures, as well as to illustrate some of the simpler mathematical techniques used in their analysis. The model contains analogs of the critical isotherm and of Maxwell’s construction. It shows hysteresis and a limiting behavior interpretable in terms of the thermodynamic limit. More importantly, it provides a description of the dynamics of a phase transition, showing a fluctuation‐induced nucleation process and the evolution of a phase transition by the motion of phase boundaries.

ISSN:0002-9505    

DOI:10.1119/1.13729

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A simple experimental apparatus is described for measurements of water density in the vicinity of 4° C, based upon a dynamic response of water to a temperature gradient.

ISSN:0002-9505    

DOI:10.1119/1.13730

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A derivation of the Doppler effect in a stratified medium based upon the phase function and Galilean transformation is proposed. The results are applied to the case of sound moving in a gas under gravity with a velocity that obeys Rayleigh’s formula.

ISSN:0002-9505    

DOI:10.1119/1.13731

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

We present an elementary derivation of high‐field ion mobility and the transverse diffusion coefficient. Our results compare favorably with the Monte Carlo investigations of Skullerud. The results are applicable when the ion drift velocityvdis much larger than the thermal velocities of the neutrals and ions. Our results are simple enough to be useful for quick estimates of the high‐field mobility and the diffusion coefficient is useful for various mass ratios.

ISSN:0002-9505    

DOI:10.1119/1.13732

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.13733

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.13734

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP