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Ugo Besson
American Journal of Physics, Volume 89, pp 909-915;

Within a vehicle in free fall, such as a spacecraft orbiting the Earth, everything appears as if there was no force of gravity: objects float and remain stationary with respect to the walls, a situation commonly described as “weightlessness.” In relativity, such a vehicle is considered an inertial reference system. In fact, this is not exactly true because of the non-uniformity of the gravitational field. Tidal effects and forces appear, and complicated motions are generated. This article examines these effects, limiting the use of complicated mathematical formalism in favor of physical reasoning. Two particular cases are treated: a spacecraft that rotates about its center of mass in sync with its orbit, so it always faces the Earth the same way, and a spacecraft that maintains the same orientation with respect to the fixed stars throughout its orbit. The static problem is solved by finding the tidal forces acting on an object at different positions within the spacecraft. The trajectories of objects released from various positions within the spacecraft are then calculated. Some concluding conceptual observations are given.
Andrei A. Snarskii, Sergii Podlasov, Mikhail Shamonin
American Journal of Physics, Volume 89, pp 916-920;

Conventional calculations of the inertia tensor in undergraduate physics course are usually done for highly symmetrical bodies. Students might therefore get the impression that the moment of inertia about any axis through the center of mass is the same only for bodies with the highest degree of symmetry relative to this point, e.g., for spheres. A simple, seemingly counterintuitive example is presented, showing that the moment of inertia of a non-regular body, here an assembly of material points, can be the same about any axis passing through its center of mass.
Scott Johnstun, Jean-François Van Huele
American Journal of Physics, Volume 89, pp 935-942;

Quantum algorithms offer efficient solutions to computational problems that are expensive to solve classically. Publicly available quantum computers, such as those provided by IBM, can now be used to run small quantum circuits that execute quantum algorithms. However, these quantum computers are highly prone to noise. Here, we introduce important concepts of quantum circuit noise and connectivity that must be addressed to obtain reliable results on quantum computers. We utilize several examples to show how noise scales with circuit depth. We present Simon's algorithm, a quantum algorithm for solving a computational problem of the same name, explain how to implement it in IBM's Qiskit platform, and compare the results of running it both on a noiseless simulator and on physical hardware subject to noise. We discuss the impact of Qiskit's transpiler, which adapts ideal quantum circuits for physical hardware with limited connectivity between qubits. We show that even circuits of only a few qubits can have their success rate significantly reduced by quantum noise unless specific measures are taken to minimize its impact.
Bradley Moser
The Physics Teacher, Volume 59, pp 552-555;

A classic, life science-themed fluid dynamics scenario is blood flow through a constriction. Physics teachers traditionally ask students if the pressure experienced by the blood in the constriction is greater, lesser, or the same as before the constriction. The conventional approach to resolving this question calls upon the equation of continuity, as well as the Bernoulli equation. Biological systems, however, experience a resistance to flow, and a consequential pressure drop, that is often better described by Poiseuille’s law. Within this apparent conflict, which approach is correct? This paper argues that Poiseuille’s law is the more appropriate choice for most biological examples and encourages a Poiseuille-first approach to teaching fluid dynamics in classes designed for life science majors.
Eliane Pereira
The Physics Teacher, Volume 59, pp 577-579;

In this article, we present a low-cost lab experience, enhanced by new technologies and easy to execute. The objective of the experiment is to explore the moment of inertia of a fidget spinner quantitatively. Our choice was to integrate the teaching of physics with the use of a popular toy, the fidget spinner, very popular among young people and children all over the world. There are several papers with teaching suggestions regarding the fidget spinner that have been developed recently. Various physical concepts can be demonstrated with the fidget spinner, for example, angular speed, torque, and moment of inertia. The experience developed here can be used by teachers from high schools, colleges, and universities.
Gisselle Dieguez, Jonathan Karpenkopf, Aaron Labrador, Ludmila Gimenez, Julian Guerra, Jack Fulton, Wojciech J. Walecki
The Physics Teacher, Volume 59, pp 556-559;

Although ripple tanks have been used in the past to perform wave simulations for electromagnetic and acoustic phenomena, especially before the advent of computers, they are still often used to demonstrate wave propagation in high school and college physics classrooms. Usually ripple tanks have a rectangular shape. The wave propagating through the tank interacts with smaller slits, reflecting surfaces, and similar objects. Sophisticated circular ripple tanks have been built in the past, but their main purpose was for the study of wave phenomena in rotating systems. John Fleming in his book describes an elliptical ripple tank, but it is not clear if he actually built one. He discusses the possibility of generating a wave at one of the focal points of an ellipse and focusing it at the other.
Xiaorong Deng, Jiarui Zhang, Qiushi Chen, Junhui Zhang, Wei Zhuang
The Physics Teacher, Volume 59, pp 584-585;

The use of sensors in smartphones to do physical experiments is a boom in the past decade, such as acceleration sensor,1,2 light sensor,3,4 magnetometer,5,6 camera,7,8 and gyroscope. However, few people study the application of proximity sensors in physical experiments, although, in our view, the employment of the proximity sensor is more accurate than other sensors (see Table I). For further research, this paper proposes a method to measure the oscillation period of a simple pendulum based on the proximity sensor integrated in the smartphone and determines the experimental value of the gravitational acceleration. Theoretical background
Antonio Augusto Soares, Ricardo Longhi Henrique
The Physics Teacher, Volume 59, pp 566-568;

Experiments using smartphones allow for teaching physics concepts in a fun and engaging way and including interdisciplinary approaches. The exploratory character of the experimental activities, along with the smartphones’ embedded technologies, when applied in the high school classroom, also has the potential to awake the students’ intrinsic motivation, contributing to more meaningful learning. Here, using two smartphones running free apps and a personal computer for data analysis, we present an experiment proposal to quantitatively study the acoustic Doppler effect in secondary schools. One of the smartphones acts as the sound source (SS) emitting a wave signal in a frequency range audible to the human being. The other one acts as the sound receiver (SR). We measured the Doppler frequency due to the relative movement between the smartphones and got good results with this frequency deviating about 1% from that one emitted by SS. This amount is large enough to be detected by SR and allows the teacher, quantitatively, to explain the physical phenomenon to the students.
Scott Lee, Joshua Thomas, Max Cooley, Richard Irving
The Physics Teacher, Volume 59, pp 548-551;

Exciting examples of physics principles illuminate the power and scope of our discipline. In this paper, we discuss a conservation of energy example for an introductory course. Energy conservation is applied to bird and dinosaur eggs to derive a method to predict the incubation period and the embryonic metabolism solely from the egg geometry. The power of this fundamental principle to yield insights into a biological example helps to demonstrate the utility of conservation of energy.
Tonya Coffey, Ross Gosky, Joshua Gregory, Raimie Neibaur, Jon Orr
The Physics Teacher, Volume 59, pp 518-520;

Exploding pumpkins with rubber bands remains a popular demonstration of the conversion of spring potential energy into kinetic energy. Videos of laughing and squealing children and adults being pelted with pumpkin fragments have millions of hits on YouTube, and the activity has even been featured on talk shows like “The Tonight Show Starring Jimmy Fallon.” This light-hearted activity is an excellent demonstration of multiple concepts in physics and engineering. In this paper, we examine and analyze a large data set collected by Jon Orr, a Canadian high school math teacher who authored a Desmos activity on learning scatter plots using this fun demo. In this paper, we expand upon Orr’s original work and explain the physics behind this activity. We analyze Orr’s data and use this analysis to explain how the number of rubber bands required to rupture a pumpkin depends primarily on the effective spring constant of the rubber band and the thickness of the pumpkin wall. We hope to provide inspiration for teachers using this demo to teach STEM concepts in the classroom.
Christopher Sirola
The Physics Teacher, Volume 59, pp 590-591;

A question for science teachers during the pandemic is: how do we actively engage students in science, given that in-person instruction will be limited at best? One lesson I use for my solar system course involves naked-eye observations of positions of celestial objects. Such activities train students to take careful measurements, keep detailed records, and comprehend three-dimensional coordinates.
Joseph Amato, Tyler Engstrom, John Essick, Harvey Gould, Claire A. Marrache-Kikuchi, Raina Olsen, , Jan Tobochnik
American Journal of Physics, Volume 89, pp 905-906;

Edward W. Walbridge
American Journal of Physics, Volume 89, pp 930-934;

It is anticipated that future skies over urban areas will be busy with drones flying back and forth delivering packages. Taking New York City as an extreme example, it is estimated that by 2026, 2600 delivery drones could simultaneously populate the city's airspace. The drone–drone collision rate of “dumb” drones can be calculated by treating them as a gas of large, randomly moving, spherical molecules, using the kinetic theory of gases. Collisions can be avoided by making each drone “smart,” i.e., by giving each a “sense and avoid” capability for detecting and avoiding a potential collision. For smart drones over New York City, the rate of potential collisions, or encounter rate, extends over a surprisingly large range: from 1 to 170,000 encounters/day, depending on input assumptions. This places stringent constraints on the probability that a smart drone encounter will result in a collision, constraints that must be met by the drone operator. Policy implications are discussed.
Jesús González-Laprea, L. J. Borrero-González, Kabir Sulca, Santiago Díaz-Echeverría, Carlos Alberto Durante Rincón
American Journal of Physics, Volume 89, pp 969-974;

This work outlines a new instructional laboratory experiment focused on the photoelectric effect and the determination of Planck's constant. The described laboratory system employs contemporary experimental techniques, including real-time data acquisition based on the use of Arduino boards. The basis of this experiment is to measure the associated turn-on voltages of a small neon bulb as it is illuminated with several different optical wavelengths. Six different LED and laser illumination sources were used with wavelengths ranging from UV (383 nm) to red (659 nm). A plot of the bulb's turn-on voltage as a function of the inverse of the excitation wavelength showed a linear relationship with a high correlation coefficient. Planck's constant was determined from this plot, yielding a value of h=7.4±1.1×10−34 J·s. Additionally, the system allows for experimental verification of the independence between excitation light intensity and the energy needed to ionize the gas inside the bulb.
Tom A. Kuusela
American Journal of Physics, Volume 89, pp 963-968;

In many optics applications, it is important to use well-polarized light. However, there are situations in which randomly polarized light has distinct advantages. We demonstrate two approaches by which a polarized light beam can be totally depolarized, each using a simple setup and inexpensive components. The first method, designed for narrow spectrum light, works by combining the horizontal polarization component of the beam with the delayed vertical component. The second method, which is most suitable for broad spectrum light, uses birefringent quartz plates. In both approaches, the polarization state is characterized by Stokes parameters measured using a rotating quarter-wave plate and fixed polarizer. We measure the coherence function of the electric fields and determine the minimum delay or quartz plate thickness required for decoherence. Coherences are modelled by Gaussian or Lorentzian functions and compared with the spectral properties of the light sources.
Tiare Guerrero, Danielle McDermott
American Journal of Physics, Volume 89, pp 975-981;

Synchronization plays an important role in many physical processes. We discuss synchronization in a molecular dynamics simulation of a single particle moving through a viscous liquid while being driven across a washboard potential energy landscape. Our results show many dynamical patterns as the landscape and driving force are altered. For certain conditions, the particle's velocity and location are synchronized or phase-locked and form closed orbits in phase space. Quasi-periodic motion is common, for which the dynamical center of motion shifts the phase space orbit. By isolating synchronized motion in simulations and table-top experiments, we can study complex natural behaviors important to many physical processes.
Said Shakerin
The Physics Teacher, Volume 59, pp 569-572;

Several new devices that demonstrate a variety of known phenomena in fluid dynamics are presented. These add on to a recent collection of demonstrations and follow the same design features as documented earlier (self-contained, easy to use, low cost). Descriptions are provided to enable replication by others, using readily available materials. The significance of each demonstration is outlined and background information on the relevant physics can be found in the cited references. The devices can be generally used in classroom lecture demonstrations, outreach activities, or other student-based projects. However, pedagogical details are left to readers’ discretion, depending on the scope of local interests and constraints. Video samples of demonstrations are available online.
Caroline Bustamante, Jacquelyn J. Chini, Erin Scanlon
The Physics Teacher, Volume 59, pp 573-576;

The number of students with disabilities and specifically students with attention-deficit hyperactivity disorder (ADHD) entering postsecondary STEM education has been increasing in recent decades. However, many instructors and popular research-based curricula are not prepared to support such learner variation. The views and experiences of people with disabilities are not uniform, either across diagnoses or within a single diagnosis, such as ADHD. Thus, individuals’ thoughts about how to support students with ADHD in physics courses will vary. We present views from one student with ADHD about strategies instructors can use to help her succeed in introductory physics courses.
David E. Meltzer
The Physics Teacher, Volume 59, pp 530-534;

Many readers of this journal are probably familiar with calls from governmental, business, and educational authorities to expand and improve the preparation of science teachers, with a particular focus on the shortage of highly qualified physics teachers. It may seem as if this problem has been around forever, and in fact similar expressions of alarm have been heard for well over a century. Why, then, does this shortage persist? Has the physics community been negligent in offering possible solutions? In fact, the opposite is true: physics educators long ago arrived at a consensus and pointed to a way forward, with a consistent set of recommendations. By tracing the history and elucidating those recommendations, we hope to help motivate physics educators to promote these goals more clearly, and with greater specificity and urgency.
Thomas B. GreensladeJr.
The Physics Teacher, Volume 59, pp 540-541;

In 1981 I published a note on “Balancers” as part of a series of illustrations drawn from 19th-century physics texts. Some months later a wonderful present arrived from a physics teacher in Japan, showing the range of our journal. This was the Horse and Rider Balancer in Fig. 1 that was just like the woodcut in my note. The little device, only 23 cm high, sits on a shelf in my museum of early physics teaching apparatus, and many visitors are drawn to it. This is a standard piece of early physics demonstration apparatus. The addition to the lead ball attached to the horse brings the center of mass below the point of suspension. Any movement from this equilibrium point raises the gravitational potential energy of the system and it oscillates until it gets into equilibrium once more.
Jean-Pierre Eckmann
American Journal of Physics, Volume 89, pp 955-962;

Mitchell Feigenbaum discovered an intriguing property of viewing images through cylindrical mirrors or looking into water. Because the eye is a lens with an opening of about 5 mm, many different rays of reflected images reach the eye and need to be interpreted by the visual system. This has the surprising effect that what one perceives depends on the orientation of the head, whether it is tilted or not. I explain and illustrate this phenomenon on the example of a human eye looking at a ruler immersed in water.
W. Dean Pesnell, Kyle Ingram-Johnson, Kevin Addison
American Journal of Physics, Volume 89, pp 943-954;

How many ways can we explore the Sun? We have images in many wavelengths and squiggly lines of many parameters that we can use to characterize the Sun. We know that while the Sun is blindingly bright to the naked eye, it also has regions that are dark in some wavelengths of light. All of those classifications are based on vision. Hearing is another sense that can be used to explore solar data. Some data, such as the sunspot number or the extreme ultraviolet spectral irradiance, can be readily sonified by converting the data values to musical pitches. Images are more difficult. Using a raster scan algorithm to convert a full-disk image of the Sun to a stream of pixel values creates variations that are dominated by the pattern of moving on and off the limb of the Sun. A sonification of such a raster scan will contain discontinuities at the limbs that mask the information contained in the image. As an alternative, Hilbert curves are continuous space-filling curves that map a linear variable onto the two-dimensional coordinates of an image. We have investigated using Hilbert curves as a way to sample and analyze solar images. Reading the image along a Hilbert curve keeps most neighborhoods close together as the resolution (i.e., the order of the Hilbert curve) increases. It also removes most of the detector size periodicities and may reveal larger-scale features. We present several examples of sonified solar data, including sunspot number, extreme ultraviolet (EUV) spectral irradiances, an EUV image, and a sequence of EUV images during a filament eruption.
B. Cameron Reed
American Journal of Physics, Volume 89, pp 927-929;

A novel graphical depiction of the relativistic barn and pole paradox is constructed in such a way that the space-time plot axes are dimensionless for both observers. Times of events over the entire range of pole-to-barn length ratio and relative speeds can be displayed in one plot for each observer. That for the barn frame clearly depicts the range of pole-to-barn length ratio over which the paradox appears, while that for the pole frame shows that the pole vaulter will only see the pole within the barn if the proper length of the pole is smaller than the contracted length of the barn.
Terry W. McDaniel
American Journal of Physics, Volume 89, pp 921-926;

A well-known problem in classical mechanics that is often presented for pedagogical purposes involves a small mass that slides without friction under a gravitational force on the surface of a sphere. Commonly, students are asked to find the angular position where a mass with no azimuthal motion leaves the spherical surface, and this question is easily within the reach of most intermediate physics students. However, a complete solution for more general motion of the mass on the spherical surface (including friction) may be suitable for many advanced undergraduates. Without friction, the problem including azimuthal motion is really an inverted version of an ideal spherical pendulum. This problem is also useful for extending discussion in classical mechanics to more sophisticated topics beyond solving Newton's laws of motion, such as the importance of conservation laws and constants of motion as they relate to symmetry, conservative versus dissipative forces, and the role of constraints.
Chris I. Larnder
The Physics Teacher, Volume 59, pp 542-543;

Today’s students are increasingly immersed in a landscape of screens and handheld digital devices through which a good deal of their interactions with the world around them are mediated. Physics educators, meanwhile, continue to rely on traditional human interactions with the physical world, such as sliding down a ramp or throwing a baseball, in order to illustrate fundamental concepts in physics. Regrettably, these interactions are decreasingly representative of the kinds of everyday activities that our students engage in, reducing their degree of engagement with the material. A new opportunity lies in the behavior of smartphones in response to sustained tilted orientations, which has for some time become a familiar mechanism of interaction between students and many of the mobile apps that they engage with on a daily basis. Here we demonstrate how a methodical investigation of this digital-era mechanism can be used to introduce the inclined plane, a standard topic in most introductory mechanics courses. We also present an open-source 3D-printed apparatus designed to support this investigation and the experiences from well over 1000 students in three different colleges.
Jake Stanley Bobowski
The Physics Teacher, Volume 59, pp 560-565;

Due to the COVID-19 outbreak, academic institutions across the globe have been forced to move to online learning environments. It has been particularly challenging for the experimental sciences to develop and deliver authentic lab-based experiences. Some of the strategies that have been adopted for first-year physics labs include: providing a video demonstration and supplying data for students to analyze, using online simulations, having students construct simple apparatuses using commonly available materials, collecting data with the aid of a smartphone, and, when dealing with smaller class sizes, providing a custom lab kit to each student. Many institutions have chosen to adopt a blend of the various strategies.
Edward F. Redish
The Physics Teacher, Volume 59, pp 525-529;

Learning to use math in science is a non-trivial task. It involves many different skills (not usually taught in a math class) that help blend physical knowledge with mathematical symbology. One of these is the idea of quantification—that physical quantities can be assigned specific numbers (with a unit). A second is to develop an intuition for scale. One way to help students develop these skills is to teach estimation: the ability to consider a physical situation and put reasonable approximate numbers to it.
Rachel M. Watson
The Physics Teacher, Volume 59, pp 588-589;

It is a sweltering June day when we drive through the Bears Ears National Monument. The dry desert scrub oak of the western slope gives way to ponderosa, grassland, and aspen groves. Flowers line the curving dirt road and the car thermometer shows a 10 °F dip. We begin our backpacking trip at the top of Woodenshoe Canyon and will end near the bottom of Dark Canyon. Accompanied by five of our student athletes and my sister, my partner and I begin our trek in the deep shade of hundred-year-old aspens and ponderosas. The cicadas sing and, with their transparent wings, alight on our backpacks.
Don Lincoln
The Physics Teacher, Volume 59, pp 521-524;

The history of particle physics can be considered nothing less than a huge triumph for science. Over the course of a little more than a century of effort, our understanding of the world of atomic and subatomic physics went from a vague understanding of atoms, to one that is much more detailed. Early in this hundred-year-long period, we learned about electrons (1897), then how they circle a dense nucleus (1911), followed by the discovery of the protons (1917) and neutrons (1932) that form the nucleus. From the 1930s onward, researchers used both cosmic rays and particle accelerators to discover antimatter (1932), and particles that don’t exist in atoms (e.g., the muon [1936] and neutrino [1956], as well as a huge number of others).
Dan Liu, Zhuojun Duan
The Physics Teacher, Volume 59, pp 544-546;

Equilibrium is an essential concept in undergraduate physics curriculum as it integrates Newton’s laws and torque. The importance also comes from its wide applications in mechanics and biomechanics. Simulations of Back and Arms are developed mainly for the undergraduates who major in physical therapy and health sciences. They are implemented as open-ended inquiry learning on the subject of key concepts in equilibrium. Students practice and apply the knowledge to calculate the forces on the erector spinae muscle and lumbar vertebrae, then conclude the optimal posture for lifting a heavy object. Besides enhancing understanding of the lecture materials, students can practice lab skills such as image analysis and control variables.
Lillian Apple, John Baunach, Glenda Connelly, Sonia Gahlhoff, Colleen Megowan Romanowicz, Rebecca Elizabeth Vieyra, Lucas Walker
The Physics Teacher, Volume 59, pp 535-539;

Multiple initiatives contend that all students should master computational thinking, including the Next Generation Science Standards, the K-12 Framework for Computational Thinking, and In turn, many physics teachers have begun to explore a variety of approaches to integrating computational modeling through programming. These activities go beyond graphical analysis tools and interactive simulations that have been a recent staple for physics educators.
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