ISSN:0002-9505    

DOI:10.1119/1.13939

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.4755907

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

Thomas Young is frequently portrayed as the reviver and main proponent of the wave theory of light in the early nineteenth century. This article shows that Young’s attitude towards the wave theory vascillated considerably owing to the changing fortunes of his ether hypothesis and his law of interference.

ISSN:0002-9505    

DOI:10.1119/1.13878

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A theory of idealized balloon flight dynamics is developed for the case of a rigidly suspended payload. A system of dynamical equations is deduced from Newton’s second law for translation and rotation. Linear perturbation theory is used to study the small oscillations of the balloon system. It is proved that the horizontal and angular degrees of freedom are coupled, while the vertical degree is independent. A cubic secular equation is derived for the complex frequency of the motion. For the case of light damping and coupling, it is shown that the frequency is determined only by inertial and geometric factors. Physical arguments are used to elucidate the mechanism of linear coupling and damping. Finally, it is shown that the second‐order vertical velocity perturbation is driven by the angular oscillation at a frequency twice as great.

ISSN:0002-9505    

DOI:10.1119/1.13879

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

Theoretical calculations are frequently simplified by setting some of the constants which occur equal to unity. The theory behind this practice is considered. It is shown that if we start with a set of dimensionally homogeneous equations, it is possible, by reducing the set of equations to an equivalent set of dimensionless equations, to assign arbitrary values to any set of dimensionally independent constants occurring in the equations. It is then shown how, after arbitrary mathematical manipulations on the resulting simpler set of equations, the equations can at any stage be restored to dimensional form with the resultant recovery of the suppressed constants.

ISSN:0002-9505    

DOI:10.1119/1.13880

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A system of BASIC and word processor computer programs has been developed to produce physics problem assignments having a different set of individualized numerical data for each student. It enables the giving of credit for homework in large class sections by reducing copying and by minimizing the effort required to grade assignments. The BASIC programs generate data and answers for each student. The word processor is used to produce the raw text of the problems, merge the text with the data, and print the resulting assignments. The system prints the student assignment sheets, instructor data and answer lists, and an instrument for rapid grading. A test of this system in two different components of a general physics course is described.

ISSN:0002-9505    

DOI:10.1119/1.13881

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

We show how the semiclassical approach to barrier penetration based on path integral methods may be generalized to handle the case that the energy of the scattered particle is greater than the height of the potential barrier.

ISSN:0002-9505    

DOI:10.1119/1.13882

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

At Reynolds numbers above about 105the aerodynamic drag force on a sphere drops sharply as the flow begins to become turbulent in the boundary layer. For baseballs, this ‘‘drag crisis’’ may occur at speeds which are typical for pitched or batted balls. The effects of the drag reduction on the behavior of both pitched and batted balls is significant, and may explain several features of the game of baseball which previously have been unexplained or attributed to other causes. In particular, the drag reduction may help to explain why pitched fastballs appear to rise, why pitched curve balls appear to drop sharply, and why home run production has increased since the introduction of the alleged ‘‘lively ball.’’ Calculations suggest that aerodynamic forces are as important a factor in fastpitch softball as in baseball, and that they are a critical factor in a number of other ball games.

ISSN:0002-9505    

DOI:10.1119/1.13883

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

A common but fascinating little toy is analyzed for its unusual oscillatory behavior. A simplified model of the toy lends itself nicely to a Lagrangian‐effective potential solution. Some results are obtained. Others are left to the interested classical mechanics student at the intermediate level.

ISSN:0002-9505    

DOI:10.1119/1.13884

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP

摘要:

The Langevin equation is a device for showing how thermal fluctuations arise in the trajectory of a classical particle which moves in a medium at nonzero temperature. One assumes a randomly fluctuating force, and a frictional force equal to a constant times the velocity. Here we generalize this approach to allow for a position‐dependent friction force, and a smooth conservative force. Instead of explicit values for the widths of the coordinate and velocity distributions (as functions of time), we find first‐order time differential equations for these widths. These equations are the same as those derivable from the Fokker‐Planck equation, in the case of narrow distributions.

ISSN:0002-9505    

DOI:10.1119/1.13885

出版商:American Association of Physics Teachers    

年代:1984

数据来源: AIP