American Journal of Physics
Am. J. Phys. 66, 583 (1998)
The harmonic oscillator propagator
Barry
R. Holstein
The Feynman propagator for the harmonic oscillator is
evaluated by a variety of path-integral-based means
American Journal of Physics
Am. J. Phys. 66, 202 (1998)
Almost rolling motion: An investigation of rolling grooved cylinders
Lawrence R. Mead and Frank W. Bentrem
We examine the dynamics of cylinders that are grooved to form
N teeth for rolling motion down an inclined plane. The grooved
cylinders are experimentally found to reach a terminal velocity. This
result can be explained by the inclusion of inelastic processes which
occur whenever a tooth hits the surface. The fraction of the angular
velocity that is lost during an inelastic collision is phenomenologically
found to be proportional to 2 sin
2 pi/
N - alpha sin
3 pi/
N, and the method of least squares is used to find the constant alpha
= 0.98. The adjusted theoretical results for the time of rolling as
well as for terminal velocity are found to be in good agreement with the
experimental results.
American Journal of Physics
Am. J. Phys. 66, 419 (1998)
Circular orbits inside the sphere of death
Kirk T. McDonald
A wheel or sphere rolling without slipping on the inside of
a sphere in a uniform gravitational field can have stable circular orbits
that lie wholly above the "equator," while a particle sliding freely
cannot.
American Journal of Physics
Am. J. Phys. 66, 753 (1998)
What is quantum mechanics trying to tell us?
N. David Mermin
I explore whether it is possible to make sense of the
quantum mechanical description of physical reality by taking the proper
subject of physics to be correlation and only correlation, and by
separating the problem of understanding the nature of quantum mechanics
from the hard problem of understanding the nature of objective
probability in individual systems, and the even harder problem of
understanding the nature of conscious awareness. The resulting
perspective on quantum mechanics is supported by some elementary but
insufficiently emphasized theorems. Whether or not it is adequate as a
new Weltanschauung, this point of view toward quantum mechanics
provides a different perspective form which to teach the subject or
explain its peculiar character to people in other fields.
American Journal of Physics
Am. J. Phys. 66, 791 (1998)
Anomalous dispersion of dye solutions observed in a prismatic cuvette
Miklos Erdelyi, Margit Hilbert, and Zsolt Bor
An experimental setup is described which uses a prismatic
dye cuvette and a dispersion glass prism. The two prisms are oriented
so as to ensure wavelength-dependent deflection in two perpendicular
planes. The dispersion of the solvent material was subtracted by using
an immersion cuvette filled with the solvent liquid of the dye solution.
The setup displays the contribution of the dye material to the
refractive index of the solution as a function of the wavelength. The
setup is simple, inexpensive, does not use toxic or hazardous materials
or high temperature ovens, and thus can be a very useful means to
demonstrate the effect of anomalous dispersion at different levels of
education.
American Journal of Physics
Am. J. Phys. 66, 718 (1998)
Introducing quantum mechanics: One-particle interferences
Valerio Scarani and Antoine Suarez
One-particle quantum interference is presented using
probably the simplest setup. This review of experimental facts may be
useful as a short self-contained introduction to quantum mechanics,
highlighting the dependence of interference on
indistinguishability.
American Journal of Physics
Am. J. Phys. 66, 772 (1998)
The sweet spot of a baseball bat
Rod Cross
The sweet spot of a baseball bat, like that of a tennis
racket, can be defined either in terms of a vibration node or a centre
of percussion. In order to determine how each of the sweet spots
influences the ³feel² of the bat, measurements were made of the impact
forces transmitted to the hands. Measurements of the bat velocity, and
results for a freely suspended bat, were also obtained in order to
assist in the interpretation of the force waveforms. The results show
that both sweet spots contribute to the formation of a sweet spot zone
where the impact forces on the hands are minimized. The free bat
results are also of interest since they provided particularly elegant
examples of wave excitation and propagation, suitable for a student
demonstration or experiment.
American Journal of Physics
Am. J. Phys. 66, 392 (1998)
Do cathedral glasses flow?
Edgar Dutra Zanotto
A general belief among members of the scientific community
is that glass articles can be bent irreversibly and that they flow at
ambient temperature. This myth is mostly based on widespread stories
that stained-glass windows of medieval cathedrals are thicker in the
lower parts. In this paper I estimate the time periods required for
glass to flow and deform at ordinary temperatures, using calculated
viscosity curves for several modern and ancient glass compositions. The
conclusion is that window glasses may flow at ambient temperature only
over incredibly long times, which exceed the limits of human
history.
American Journal of Physics
Am. J. Phys. 66, 14 (1998)
Causality and negative group delays in a simple band pass amplifier
Morgan W. Mitchell and Raymond Y. Chiao
We demonstrate a bandpass amplifier which can be constructed
from common electronic components and has the surprising property that
the group delay is negative in most spectral regions. A pulse
propagating through a chain of such amplifiers is advanced by several
milliseconds: the output waveform precedes the input waveform.
Although striking, this behavior is not in conflict with causality,
as demonstrated by experiments with pulses which start or
end abruptly.
American Journal of Physics
Am. J. Phys. 66, 724 (1998)
Materials physics: A new contemporary undergraduate laboratory
Herbert Jaeger
Michael J. Pechan and Daniel K. Lottis
We have developed a laboratory course focusing on the
physics of materials. This course, taught in place of a "conventional"
lecture-only solid state or condensed matter physics course, helps
prepare students for the technical work force and also serves as a
solid, broad-based foundation for students bound for graduate school.
In addition, the course illustrates the increasingly interdisciplinary
nature of physics. Classroom activities and experiments concentrate on
four materials classes: metals, ceramics, semiconductors, and polymers.
Experiments include electrical conductivity of metals and
semiconductors; ionic conductivity of ceramics; superconductivity in
metals, alloys and ceramics; preparation and characterizations of
metallic thin films; scanning tunneling microscopy; magnetic properties
of materials; impedance spectroscopy of solid electrolytes; phase
diagram determination by differential thermal analysis and x-ray
diffractometry; Hall effect in pure and doped semiconductors; dielectric
response of polymers; and mechanical properties of
polymers.
American Journal of Physics
Am. J. Phys. 66, 810 (1998)
Propagation of a Feynman error on real and inertial forces in rotating systems
Martin S. Tiersten and Harry Soodak
Serious errors and misleading statements concerning real and
inertial forces in rotating coordinate systems in The Feynman
Lectures on Physics are pointed out and corrected.
American Journal of Physics
Am. J. Phys. 66, 797 (1998)
Who were Fabry and Perot?
Joseph F. Mulligan
IN 1897 Charles Fabry and Alfred Perot published their most
important article on what we now call the Fabry-Perot interferometer.
Despite the great importance of this instrument for present-day research
in physics and astrophysics, its inventors are almost completely unknown
to most physicists. This article presents brief accounts of the life
and work of Fabry and Perot, who at the beginning of the twentieth
century were highly regarded by physicists throughout the world for
their contributions to astrophysics, including Fabry's 1913 discovery
(with Henri Buisson) of the ozone layer in the Earth's
atmosphere.
American Journal of Physics
Am. J. Phys. 66, 34 (1998)
Approximate trajectories for projectile motion with air resistance
Michael A. B. Deakin and G. J. Troup
To remarkable accuracy and under a wide variety of
conditions, the trajectories of projectiles under various laws of
resistance may be approximated by cubic curves. This allows for the
relatively simple calculation of many details of the flight
American Journal of Physics
Am. J. Phys. 66, 377 (1998)
Quantum measurement theory and the Stern-Gerlach experiment
M. Hannout, S. Hoyt, A. Kryowonos and A. Widom
The Stern-Gerlach experiment was one of the early
illustrative examples of the Bohr view of quantum mechanics. In the Bohr
view, a measurement is an interaction between a quantum object and an
apparatus which acts in classical fashion. There are still open problems
with this concept many of which enter into the discussion of the original
Stern-Gerlach measurement.