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Coupled oscillations of the Wilberforce pendulum unveiled by smartphones
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| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 11) |
| Halaman | : | 873–878 |
| Abstrak | : | The Wilberforce pendulum illustrates important properties of coupled oscillators including normal modes and beat phenomena. When helical spring is attached to a mass to create the Wilberforce pendulum, the longitudinal and torsional oscillations are coupled. A Wilberforce can be constructed simply from a standard laboratory spring, and a smartphone's accelerometer and gyroscope can be used to monitor the oscillations. We show that the resulting time-series data match theoretical predictions, and we share the procedures for observing both normal modes and beats. |
The first Global e-Competition on Astronomy and Astrophysics
| Pengarang | : | Patrice Venturini |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 11) |
| Halaman | : | 867–872 |
| Abstrak | : | The first global e-competition on astronomy and astrophysics was held online in September–October 2020 as a replacement for the International Olympiad on Astronomy and Astrophysics, which was postponed due to the COVID-19 pandemic. Despite the short time available for organization, 8 weeks, the competition was run successfully, with 325 students from over 42 countries participating with no major issues. The feedback from the participants was positive and reflects the ways in which such events can boost interest in astronomy and astronomy education. With online activities set to become more prevalent in the future, we present an overview of the competition process, the challenges faced, and some of the lessons learned, aiming to contribute to the development of best practices for organizing online competitions. |
Using lock-in detection to build a barcode scanner
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 1023–1030 |
| Abstrak | : | Lock-in detection is a widely used experimental technique in which a weak signal is measured by modulating it at a particular frequency. Then, by detecting an experimental output at that frequency, the desired signal can be isolated from much larger-amplitude noise. Here, we report on the implementation and optimization of a homemade laser barcode scanner based on the lock-in technique. Our setup is comprised of components that are readily available in an undergraduate instructional laboratory. The successful transcription of the barcode into a digital signal was achieved, and this digital signal was collected with a simple computer and processed to reveal the encoded number. |
Molecular spectroscopy as a laboratory experiment: Measurement of important parameters of sodium diatomic molecules
| Pengarang | : | Md Shakil Bin Kashem |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 1015–1022 |
| Abstrak | : | We present an inexpensive sodium molecular spectroscopy experiment for use in an advanced undergraduate laboratory course in physics or chemistry. The molecules were excited predominantly from the ground (?  = 15) state to the (?  = 6) state using a commercially available 532-nm broadband diode laser. The laser-induced molecular fluorescence was measured using a miniature fiber-coupled spectrometer at a resolution of 0.5 nm. The spectral peak assignments were done by comparing the observed spectrum with the calculated Franck–Condon values. Important molecular constants such as fundamental frequency, anharmonicity, bond strength, and dissociation energy of the ground electronic state were determined by using the Birge–Sponer extrapolation method. The presence of highly visible blue glowing molecules along the green laser beam creates an engaging laboratory experience. Emphasis is placed on students developing their understanding of the molecular structure, practicing molecular spectroscopic techniques, and applying knowledge of light–matter interactions to a physical system. |
Pandemic modeling with the game of life
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 1008–1014 |
| Abstrak | : | The generalized semi-classical game of life (gSCGOL) is a cellular automaton in which qubits evolve through repeated applications of birth, death, and survival operators. gSCGOL is used to model human–virus interactions during the COVID-19 pandemic by using cell “liveness” to be equivalent to the human population that is vulnerable to the disease. A match to the United Kingdom (UK) daily 7-day average COVID-19 deaths was achieved by daily changes to a parameter V representing the vulnerability of the population to the virus. The model predicts that the first COVID-19 virus entered the UK on December 22, 2019 with an uncertainty of days. The changes in the vulnerability V elucidate the human response to the unfolding pandemic during 2020, quantifying the impact of the lockdown, the relaxation of restrictions, and the opening and closing of schools. The model predicts that starting the first UK national lockdown one week earlier would have led to 40% fewer COVID-19-related deaths, equivalent to 17 000 lives. |
Numerical simulation of mirages above water bodies
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 999–1007 |
| Abstrak | : | A mirage or fata morgana is typically an upside-down “mirror” image of a scenery in deserts, over sun-heated roads, or above bodies of water. When the temperature gradient of air is large, as can happen near a surface, it results in a large gradient of the density and the refractive index as a function of height. Mirages appear when light travels through a medium with a gradient in its refractive index and, therefore, get bent towards the higher values, generating reflected images. A computer program that simulates mirages above water using the method of ray tracing has been developed and is presented here in detail for educational purposes. Results on the effect are shown by simulated images for various water-air temperature-difference cases with values ranging from 5 to 0 °C. Comparison of the simulations to a real-life scenario at Lake Balaton, Hungary has also been provided. |
Metastable states in a 1D quantum system
| Pengarang | : | John Eric Goff |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 993–998 |
| Abstrak | : | One-dimensional (1D) systems in which metastable states exist are physically important, but they are usually not discussed quantitatively in textbooks. This paper presents a relatively simple 1D system involving a piecewise-constant potential for which metastable states can be easily calculated using a computer algebraic system. The metastable-state wave functions are computed and plotted for various particle energies. The Breit–Wigner approximation is used to fit the resulting resonant structure in the transmission coefficient. Connections are made between the initial analysis and poles of the scattering matrix that corresponds to the potential. |
Thermal physics in the data age—Students judge the applicability of the equipartition theorem
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 988–992 |
| Abstrak | : | Providing students of introductory thermal physics with a plot of the heat capacities of many low density gases as a function of temperature allows them to look for systematic trends. Specifically, large amounts of heat capacity data not only allow students to discover the equipartition theorem but also point to its limited applicability. Computer code to download and plot the temperature-dependent heat capacity data is provided. |
Nonlinear oscillator acceleration and period variation with amplitude
| Pengarang | : | Peter F. Hinrichsen |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 979–987 |
| Abstrak | : | A classic nonlinear spring mass oscillator, the nonlinearity of which could be varied by changing the initial stretching of the spring, was used to investigate how the amplitude dependence of the period and the harmonic content depended on the nonlinearity. The oscillations were measured with a photogate and a MEMS accelerometer, allowing both the oscillation period and the Fourier components of the motion to be precisely determined. The results were in good agreement with theory. |
Teaching rotational physics with bivectors
| Pengarang | : | Steuard Jensen |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 91 (No. 12) |
| Halaman | : | 970–978 |
| Abstrak | : | Angular momentum is traditionally taught as a (pseudo)vector quantity, tied closely to the cross product. This approach is familiar to experts but challenging for students, and full of subtleties. Here, we present an alternative pedagogical approach: angular momentum is described using bivectors which can be visualized as “tiles” with area and orientation, and whose components form an antisymmetric matrix. Although bivectors have historically been studied in specialized contexts like spacetime classification or geometric algebra, they are no more complicated to understand than cross products. The bivector language provides a more fundamental definition for rotational physics and opens the door to understanding rotations in relativity and in extra dimensions. |