ISSN:0002-9505    

DOI:10.1119/1.12367

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.12372

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

ISSN:0002-9505    

DOI:10.1119/1.1807216

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

We have performed a straightforward vertical fall experiment for a case where the effects of air resistance are important and directly measurable. Using a commonly available badminton shuttlecock, a tape measure, and a millisecond timer, the times required for the shuttlecock to fall given distances (up to almost ten meters) were accurately measured. The experiment was performed in an open stairwell. The experimental data was compared to the predictions of several models. The best fit was obtained with the model which assumes a resistive force quadratic in the instantaneous speed of the falling object. This model was fitted to the experimental data enabling us to predict the terminal velocity of the shuttlecock (6.80 m/sec). The results indicate that, starting from rest, the vertically falling shuttlecock achieves 99% of its terminal velocity in 1.84 sec, after falling 9.2 m. The relative ease in collecting the data, as well as the excellent agreement with theory, make this an ideal experiment for use in physics courses at a variety of levels.

ISSN:0002-9505    

DOI:10.1119/1.12373

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

For a collection of moving sources with velocities randomly distributed, the classical Doppler effect predicts that half of the sources appear redshifted and half appear blueshifted. When relativistic speeds are involved, the transverse Doppler effect introduces a preponderance of redshifts over blueshifts. In this article it is shown that the size of the effect (i.e., the ratio of redshifts to blueshifts) can be calculated in a straightforward manner. For quasars, redshifts as large as 3.5, corresponding to velocities of 0.91c, have been observed. At this speed, randomly directed motions will produce almost an order of magnitude more redshifts than blueshifts. This consideration should be mentioned in discussions of whether quasars are ’’local’’ rather than ’’cosmological’’ objects.

ISSN:0002-9505    

DOI:10.1119/1.12374

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

An easy‐to‐use set of programs for the computerized generation of multiple‐choice and essay examinations in an introductory astronomy course is described. The programs allow the user to establish files of test questions and to rapidly assemble printed copies of examinations suitable for photocopying. Written in ALGOL for a Burroughs B6700 computer, the programs can, in principle, be implemented on large mainframe computers or on microcomputers of a size increasingly available to physics departments. The advantages and costs of computerized test generation are discussed.

ISSN:0002-9505    

DOI:10.1119/1.12055

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

A recycling oscillator has been designed in which a fiber optic data link closes the loop. The repeated emission and detection of infrared pulses is termed a ’’wink‐around system’’ in correspondence with the sing‐around methods used in ultrasonics. Electronic delay elements reduce the system frequency to about a megahertz. The difference in period for two fiber lengths yields a value for the speed of light in the cable.

ISSN:0002-9505    

DOI:10.1119/1.12375

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

We consider the electrostatic problem of a point charge in a domain bounded by conducting planes. We list all such domains for which a solution by images exists, describe the image charge arrays in familiar crystallographic terms, and give an illustrative example. We also give an account of the methods used to arrive at the allowed domains and their corresponding solutions.

ISSN:0002-9505    

DOI:10.1119/1.12376

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

Electrostatic laws are obtained for charges constrained to lie in a plane. The corresponding electric field E in the plane obeys neither Poisson’s equation nor Gauss’ law. A vector field Λ is constructed which does satisfy these equations and which is a functional of the charge density. Various limiting forms of the coupling dyadMare obtained. where E=MΛ.

ISSN:0002-9505    

DOI:10.1119/1.12377

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP

摘要:

The cohesive energies of the alkali metals are calculated, using a description based on the free electron model, to within to 0.1 eV of the experimental values. Also it is shown that for lithium metal the electron kinetic energy is comparable in magnitude to the energy associated with the repulsive interactions over a substantial range of lattice spacing. The method used is considered to be appropriate for presentation to undergraduate students in materials science and related courses.

ISSN:0002-9505    

DOI:10.1119/1.12056

出版商:American Association of Physics Teachers    

年代:1980

数据来源: AIP