These brief summaries are designed to help readers easily see which articles will be most valuable to them. The online version contains links to the articles.

Regular readers will note the temporary increase in the length of the issue as we try to decrease the backlog of manuscripts. We think the end is in sight.

Jacob Katriel

89(6), p. 557

https://doi.org/10.1119/10.0004956

Since the number of quantum-mechanical potentials that can be solved exactly is limited, approximation methods are important. In this paper inspired by Sanjoy Mahajan’s “Back of the Envelope” treatment of power-law potentials (June 2020), the author shows how the Bohr quantization condition mvr = n can be used to determine the dependence of energy levels on the quantum number n for spherically symmetric potentials. Results are exact for the hydrogen atom, harmonic oscillator, and the infinite square well, and asymptotically correct for the linear potential. This treatment is suitable for both beginning and more advanced students.

Eric M. Edlund

89(6), p. 559

https://doi.org/10.1119/10.0003489

The analysis of intercept and rendezvous of two spacecraft is mathematically challenging and is typically tackled by solving multiple differential equations. In this article, the author sidesteps these complications by choosing a geometry-based approach, making the topic suitable for the junior level mechanics course. An HTML JavaScript orbit calculator is also provided so that students (and their instructors!) can easily test their calculated solutions and strengthen physical intuition.

Mohammad-Reza Alam

89(6), p. 567

https://doi.org/10.1119/10.0003512

You may have idly wondered why partially blocking a hose outlet makes the water shoot out faster, and then carelessly assumed that it had something to do with keeping the mass flow rate constant. But, of course, there’s no law of conservation of mass flow rate. Read this paper to find a better explanation. You’ll find not only a simple physical intuition and use of dimensional analysis, but also a treatment of fluid dynamics at a level appropriate for upper-level undergraduates in physics or engineering.

Tianyi Guo, Xiaoyu Zheng, and Peter Palffy-Muhoray

89(6), p. 575

https://doi.org/10.1119/10.0003819

Imagine this. On a nice summer day, you have just watered your plants with a garden hose. You close the water inlet valve and then, before coiling up the hose, you release the water pressure by opening the outlet valve. As you watch, the garden hose spontaneously curves into a sinusoidal shape. This paper shows how the helical angle of the hose’s reinforcing mesh causes it to elongate upon pressure release. When it elongates, the hose will then spontaneously exhibit a buckling instability, which is responsible for its undulating shape. This effect has interesting consequences for the rigidity of hydroskeletons–fluid-filled tubes reinforced by helical filaments–in nature. This article provides a fun application of Euler’s self-buckling instability for undergraduate mechanics lectures or labs.

Karl C. Mamola and William A. (Toby) Dittrich

89(6), p. 583

https://doi.org/10.1119/10.0003877

In a paper well suited to a first semester college physics course, analysis (without calculus) and video are used in a discussion of the loss of mechanical energy of a ball as it follows the loop-the-loop motion of a frequently used mechanics demonstration. Readers may be surprised to see the large effect of jerk, that is, the sudden change in the acceleration, even though the track is smooth. The above link will also take the reader to the article’s video abstract.

Vijay A. Singh and Arnav Singh

89(6), p. 589

https://doi.org/10.1119/10.0003920

Clearer skies due to the pandemic-induced lock-down inspired a fresh look at reported sightings of Himalayan peaks in the historical record. This pedagogical article can inspire problems for undergraduate students.

Matthew J. Farrar

89(6), p. 596

https://doi.org/10.1119/10.0004856

This paper shows how Arduino™ microprocessors can be used within a modeling lab framework to eliminate the “black box” aspect of data collection in the introductory lab.

Juliette Plo, Dihya Sadi, Elio Thellier, Pawel Pieranski, Mehdi Zeghal, and Patrick Judeinstein

89(6), p. 603

https://doi.org/10.1119/10.0003350

An experiment is described in which the Fréedericksz transition, a phase transition involving liquid crystals, can be seen as well as heard in a classroom setting. The experiment uses a twisted nematic display as the capacitor in an RC oscillator circuit. Changes in the oscillator frequency are induced by applying magnetic and electric fields and detected using a software-defined radio. Extensive supplementary materials show how to re-create the experiment. The above link will also take the reader to the article’s video abstract.

Luis Oscar González-Siu, Martha Rosete-Aguilar, and Neil C. Bruce

89(6), p. 612

https://doi.org/10.1119/10.0003427

An algorithm is presented to help students and teachers visualize the propagating electromagnetic field in uniaxial and biaxial crystals. This algorithm is implemented with Mathematica and can be useful in electrodynamics and optics courses at the undergraduate and graduate level.

Ben Kain

89(6), p. 618

https://doi.org/10.1119/10.0004835

This illustration of a useful quantum computing algorithm can be presented to undergraduate students who have not yet completed a quantum mechanics course, and includes code that can be run on IBM’s quantum computers.  The demonstration uses Grover’s search algorithm, which searches an unsorted database faster than a classical algorithm.  The standard presentation is expanded to produce a more satisfying and useful solution.

Aparajita Bhattacharyya, Jayanta K. Bhattacharjee, and Debabrata Sinha

89(6), p. 627

https://doi.org/10.1119/10.0003397

The time evolution of a Gaussian wave packet is evaluated in three potentials using the Heisenberg approach instead of the normal Schrödinger approach. Instructors of quantum mechanics will gain insight from this paper and may choose to develop problems to help their students better understand time evolution of wave functions.

Anna P. Czarnecka and Andrzej Czarnecki

89(6), p. 634

https://doi.org/10.1119/10.0003448

Free fall in a gravitational field is explained as the effect of refraction of the quantum mechanical wave function due to time dilation. Read that sentence again. Then read the article.

Matteo Luca Ruggiero

89(6), p. 639

https://doi.org/10.1119/10.0003513

The study of gravitational waves has never been more topical than in the past decade, but the textbook treatment of gravitational waves remains intimidating.  In this article, the physics of gravitational waves is explored through the use of an electromagnetic analogy which allows the reader more direct access to the waves’ physical effects on detectors.  The article is appropriate for advanced undergraduates, graduate students, and faculty who are keen to develop an intuitive sense of gravitational waves.

Rebekah Aguilar, Patrick Powers, Nina Abramzon, and P. B. Siegel

89(6), p. 647

https://doi.org/10.1119/10.0003490

This paper shows how students can use a 2-in. NaI detector to measure the main sources of terrestrial gamma radiation in their environment, i.e., the 40K, 238U and 232Th decay series, and learn how to calibrate the detector for efficiency and sample self-absorption. This apparatus allows the experiments to be performed over two three-hour laboratory sessions so that even students in lower-level courses can learn about natural radiation in the environment.

Harvey S. Leff, Reviewer

89(6), p. 655

https://doi.org/10.1119/10.0004331