These brief summaries are designed to help readers easily see which articles will be most valuable to them. Starting with this issue, the editor who oversaw the manuscript's review and wrote the summary is included in the byline. The online version contains links to the articles.

Ugo Besson

89(10), p. 909

When an astronaut releases an object from rest within an orbiting spacecraft, its ensuing motion can appear quite complicated. In this article, the author derives the equations of motion in the spacecraft's reference frame (called the Clohessy–Wiltshire equations) in a straightforward, physically intuitive way, completely sidestepping the need for advanced mathematics and, thereby, rendering the treatment suitable for an undergraduate mechanics course. Using these equations, the author shows how simple springs, rods, balls confined to tubes, and balloons can provide an astronaut with valuable information about the spacecraft's orbit. In addition, he discusses the relevance of the equations to spacecraft rendezvous, extra-vehicular activities, and the earthbound phenomenon of ocean tides.

Andrei A. Snarskii, Sergii Podlasov, and Mikhail Shamonin

89(11), p. 916

A quick poll amongst your students—or even your colleagues—should convince you that getting an intuitive grasp of moments of inertia is not easy. This paper may help with this. First, it offers a simple and elegant way of proving that a cube has the same moment of inertia, whatever axis is considered, provided it passes through its center of mass. It also gives an example of a non-symmetrical body that, counter-intuitively, has an isotropic moment of inertia tensor. This makes a nice brain-teaser for your undergraduate classical mechanics class.

Terry W. McDaniel

89(10), p. 921

Most readers will think that they are familiar with the problem of a mass sliding on a sphere. However, what if there's friction? What if the mass starts from a point other than the top and has an initial velocity in the azimuthal direction? This problem presents a rich playground of mechanics problems and is particularly well suited for computational assignments.

B. Cameron Reed

89(10), p. 927

A novel, nondimensionalized version of the barn and pole paradox is presented, showing advanced students how an experienced physicist might approach this classic problem. Instructors will also find a “recipe” for parameter sets that led to paradoxes. Short and sweet!

Edward W. Walbridge

89(10), p. 930

If the predictions made by companies, such as Amazon, hold true, more than 50% of parcel deliveries will be made by drone aircraft within the present decade. The skies above major cities will be abuzz (literally) with swarms of delivery drones, and the average separation between them could be as low as 140 m. In this article, the author uses kinetic theory to estimate the surprisingly high collision rate between hypothetical “dumb” drones, which have no collision avoidance capability, and discusses the required reliability of such systems to ensure safe operation.

Scott Johnstun and Jean-François Van Huele

89(10), p. 935

Useful quantum computing algorithms have been developed over the past few decades with theoretical, idealized devices in mind. Due to the recent rapid progress in quantum technologies, there are now many types of real quantum computing hardware available, some that contain more qubits can be easily simulated on a laptop and so contain potential to perform truly useful computations. However, these real devices come with important limitations due to noise and qubit connectivity. For students of quantum computing, learning about the limitations of real physical devices will be essential for doing useful work in the field. This paper discusses Simon's algorithm and uses IBM's publicly available Qiskit platform to compare the results of running the algorithm on both real and simulated devices.

W. Dean Pesnell, Kyle Ingram-Johnson, and Kevin Addison

89(10), p. 943

Sometimes, we want not only to see our data but also to hear it. Sonifying data can reveal new patterns and information, and they can also make data accessible to people with vision impairments. However, attempts to sonify data, particularly 2D images, lead to many questions and options, which this paper introduces in a way that will be useful both to those who want to increase the accessibility of science and for those looking for interesting student projects that may reveal new trends in data.

Jean-Pierre Eckmann

89(10), p. 955

This paper tells you how to introduce your undergraduate students to caustics with a bucket full of water and a ruler. If a ruler is immersed into water, the image your eye sees can seem to come from two different source points, located on two different caustics. The brain selects what it perceives as the sharpest one, depending on the astigmatic correction it makes, which, in turn, is determined by the orientation of your head. As a consequence, when tilting the head, about 80% of people perceive that the ruler is moving in the water. This makes for a fun class demonstration. This paper is also a tribute to Mitchell Feigenbaum, one of the pioneers of chaos theory, who spent his last few years working on caustics and anamorphoses.

Tom A. Kuusela

89(10), p. 963

We are all familiar with ways to produce a polarized light beam from an unpolarized source. However, some optics applications require the opposite: How do you produce an unpolarized beam from a polarized source? In this article, the author shows how to exploit the finite bandwidth of the source to depolarize it completely. The apparatus used to achieve this and to measure the polarization state of the beam is simple, inexpensive, and easy to understand, making it well-suited for use in undergraduate (or graduate) optics laboratories.

Jesús González-Laprea, L. J. Borrero-González, Kabir Sulca, Santiago Díaz-Echeverría, and Carlos Alberto Durante Rincón

89(10), p. 969

Measuring the turn-on voltage of a conventional neon bulb enables the observation of the photoelectric effect in a low-cost experiment. Instructions are given for performing the experiment using a combination of LEDs and lasers as photon sources.

Tiare Guerrero and Danielle McDermott

89(10), p. 975

The authors use simple molecular dynamics simulation to show how the motion of a single particle can become synchronized to environmental and external forces, providing insight into the behavior of a number of condensed matter systems.

Robert Frederik Diaz Uy

89(12), p. 982

The original formulation of Lagrangian mechanics accounts only for conservative forces. Many students are not aware that Lagrange methods can still be used in the presence of non-conservative effects, such as friction and variable masses. This paper uses a momentum flux term in the Euler–Lagrange equation to describe the oscillations of a variable mass of liquid in a drinking straw subject to a damping force as it flows into and out of a bath, eventually settling at the bath level. This paper is a follow-up to a previous paper published here, describing a laboratory experiment and Newtonian analysis of the same problem.