Vol. 65 No. 2 Jul-Dec (2019): Revista Mexicana de Física E

In this paper we will use classical field theory to address the interaction of an accelerated point source with a non-massive Klein-Gordon-Fock (KGF) field in Minkowski spacetime. For this, initially, we obtain the KGF equation for the non-massive scalar field via lagrangian formalism and the scalar potential through Green's function formalism. Finally, we reach the expression of the power radiated by a point scalar source under the influence of this field and its covariant generalization.

Nowadays, methodologies coming from studying physical systems are being applied to the description of a wide variety of complex systems. In particular, one can study thermodynamical methods to describe the overall behavior of many systems, independent of the precise microscopic construction. In this paper, a real Mexican highway is studied as a cellular automata system using available official data released by the Mexican Government. The system studied is the Cuernavaca bypass which was modified in 2016. Official data allows to compare the highway before and after the modifications. As more complex thermodynamic variables such as entropy is difficult to define and measure in discrete traffic models, it is shown how other more simple variables such as the standard deviation can be enough to have a complete analysis of the system. More specifically, it is shown how standard deviation can be seen as a measure of order. Results from the study of the highway show how, taking a minimal measure such as ordering the transit of heavy trucks can reduce up to 30\% the travel time from one end to another. Otherwise, travel times stays practically constant with respect to the original system.

This paper analyzes the translational motion that a sphere rolling over an azimuthally symmetric surface, under the presence of a constant gravitational field, and with the rolling-without-slipping condition, exhibits in two different situations: with and without friction with air, where the latter is expressed as a power-series function of the sphere’s translational speed. In order to achieve this, the equations of motion for each case are obtained through the use of Lagrangian Mechanics and are subsequently solved by numerical computation in Wolfram Mathematica. For the frictionless case, periodic behavior and a conservation law for the angular coordinate have been found, along with the condition under which an effective potential energy can be approximated as well as the relationships between initial conditions that produce gravitational-like trajectories for the motion of the sphere. The equations of motion derived for the case with friction are found to predict the energy loss and general decay of the sphere’s motion. Likewise, the normal force over the sphere as a function of time is obtained through the method of Lagrange's Undetermined Multipliers, and thus, the general conditions that the motion must satisfy in order to be described by the obtained models. Overall, this research provides insight into the type and characteristics of the motion performed by the system in these two cases, both through equations and their numerical solutions for different surfaces and initial conditions.

We give some examples of the application in classical mechanics of the double and the dual numbers, which are analogous to the complex numbers.

Como es sabido, la fuerza de roce estático depende de las fuerzas aplicadas, mientras que la fuerza de roce cinético es constante e independiente de dichas fuerzas. Gráficamente, esto significa que la relación entre fuerza de roce y fuerza aplicada es una recta ascendente para el caso estático, y una recta horizontal para el caso cinético. Esta situación, que se estudia teóricamente en todos los cursos introductorios de mecánica newtoniana, tanto en educación secundaria como superior, pocas veces es analizada experimentalmente con los estudiantes. En este trabajo se presenta un sencillo experimento que permite obtener una gráfica roce vs fuerza aplicada que se encuentra en excelente acuerdo con la gráfica teórica (esperada) que aparece en la mayor parte de los textos de estudio de física. Se trata de un experimento simple y fácil de implementar, destinado principalmente a estudiantes universitarios de ciencias e ingeniería que siguen un primer curso de mecánica newtoniana.

El “Test of Understanding of Graphs in Kinematics (TUG-K)”, es el test de opciones múltiples más importante diseñado hasta la fecha para evaluar el entendimiento de estudiantes universitarios en gráficas de cinemática. En este estudio se presenta una modificación significativa de este test en español. El test fue implementado en 124 estudiantes que terminaban un curso de mecánica basado en cálculo en una universidad privada mexicana. Los cuatro objetivos del presente artículo son: (1) presentar el test en español y su proceso de rediseño, (2) mostrar que es un instrumento de evaluación confiable con poder discriminatorio adecuado, (3) exponer un análisis detallado del entendimiento de los estudiantes en los conceptos evaluados en el test, y (4) establecer recomendaciones específicas, basadas en los análisis previos, para la instrucción de estos conceptos. De esta forma, este artículo ofrece un análisis exhaustivo de dificultades de entendimiento, recomendaciones basadas en investigación y un examen disponible en el apéndice que pueden ser empleados por investigadores del área de la enseñanza de la física, y por profesores que enseñen el tema de gráficas de cinemática en cursos de física en países hispanohablantes.

 

 

 

The “Test of Understanding of Graphs in Kinematics (TUG-K)”, is the most important multiple-choice test designed to date to evaluate the understanding of university students in kinematics graphs. In this study, we present a significant modification of this test in Spanish. We administered the test to 124 students who finished a mechanics-based course in a private Mexican university. The four objectives of this article are: (1) to present the test in Spanish and its redesign process, (2) to show that it is a reliable evaluation instrument with adequate discriminatory power, (3) to present a detailed analysis of students’ understanding on the concepts evaluated in the test, and (4) to establish specific recommendations, based on the previous analyzes, for the instruction of these concepts. In this way, this article offers a comprehensive analysis of understanding difficulties, research-based recommendations and the test available in the Appendix that can be used by researchers
in the field of physics education, and by teachers who teach the subject of graphics of kinematics in physics courses in Spanish-speaking countries.

 

 

Hasta el año 1974, el estudio de los agujeros negros estuvo bajo la hegemonía de la relatividad general de Einstein. Sin embargo, ese mismo año, Stephen Hawking incorporó la mecánica cuántica y descubrió que los agujeros negros tienen temperatura, entropía, y se evaporan. Estos tres grandes descubrimientos marcaron el nacimiento de lo que ahora podemos denominar agujeros negros cuánticos, en oposición a los agujeros negros clásicos, cuya descripción se basa únicamente en la relatividad general. El presente trabajo busca proporcionar una introducción a los tres grandes descubrimientos de Hawking, accesible a estudiantes no graduados de ciencias e ingeniería.

 

 

Until 1974, the study of black holes was under the hegemony of Einstein’s general relativity. However, that same year, Stephen Hawking incorporated quantum theory and discovered that black holes have temperature, entropy, and evaporate. These three great discoveries marked the birth of what we can now call quantum black holes, as opposed to classic black holes, whose description is based only on general relativity. The present work seeks to provide an introduction to the three great discoveries of Hawking, accessible to undergraduate students of science and engineering.

 

 

Handling coherent states by undergraduates students may be
a hard task, as they have to deal with Glauber's series $e^{-\frac {|\alpha|^2} {2}}\sum\limits_{n=0}^\infty\frac {\alpha^n} {\sqrt{n!}}\phi_n(x)$. We show here that the task can be greatly simplified by introduction of a novel compact formula for Glauber coherent states employed in [ Int. J. Mod. Phys. B {\bf 31} (2017)
175051]. This expression is obtained by solving the basic
differential equation associated to coherent states $a|\alpha>=\alpha|\alpha>$.

The pre-post instruction answer dynamics to the research-based, multiple-choice, single-response test DIRECT, has been used to study the effect of traditional and active learning pedagogies on gains and losses of conceptual knowledge induced by instruction. Our results suggest that, for high school students of a Latin American education system and on the subject of simple DC electric circuits, these features seem to be strongly influenced by the teaching approach.  In particular our data suggest that the active learning strategy Tutorials in Introductory Physics is clearly more efficient that traditional instruction, increasing by a factor of two the gain induced by instruction and furthermore, decreasing losses by a similar factor. It is also found that, even using this successful teaching methodology, an important fraction of students need further actions to acquire sought scientific knowledge. It is suggested that reinforcing this instruction with a few, but pedagogically coherent, active-learning activities could further improve learning outcomes, improving therefore the efficiency of instruction to boost conceptual learning, a much needed challenge for science education in most Latin American countries.

Se analizan teórica y experimentalmente las oscilaciones unidimensionales no lineales de un imán que está unido a un resorte e interactúa
con un grupo de imanes. Se resuelve numéricamente la ecuación de movimiento del sistema utilizando el método de Euler en una planilla
de cálculo. Experimentalmente, la evolución temporal de la posición se obtiene mediante análisis de video. La correspondencia entre las
predicciones del modelo y los datos experimentales deja en evidencia la potencialidad de las herramientas utilizadas. La sencillez de la
propuesta presentada permite su aplicación en los primeros cursos universitarios de Física experimental.

 

The one-dimensional nonlinear oscillations of a magnet attached to a spring and interacting with a set of magnets are analyzed theoretically
and experimentally. The equation of motion is solved numerically using the Euler method in a spreadsheet. The temporal evolution of the
position is obtained using video analysis. The correspondence between the data and the predictions of the model shows the potential of the
tools employed. The simplicity of the approach allows its application in the first university courses of experimental Physics.

 

 

 

In this work, we emphasize that it is possible using a personal computer to perform a Monte
Carlo simulations in a reasonable computing time, and find the equilibrium structure of a hardsphere gas for a Euclidean multi-dimensional spaces. We study the properties of equilibrium and determine the equation of state of gas of hard spheres in Euclidean spaces from two to seven dimensions. The results show that the pressure is in agreement with different theoretical models based on virial expansion in spaces from two to five dimensions, also our results are extended for seven dimensions. As expected, it was found that the system of hard spheres loses its structure and the pressure of the system decreases when the dimension of the space increases.

The Lagrangian formulation has been an extensive tool for the analysis of physical systems. In particular, we have applied the Lagrangian procedure to deduce the dynamics and stability for an electric pendulum system. We have considered two cases, a repulsive and attractive electric interactions as perturbations to the classical simple pendulum model. We study both cases, the repulsive and attractive electric interactions that can be considered as perturbations to the classical simple pendulum model. We have contrast both situations studying their restrictions, phase trajectories and stability points for this purpose.

In this paper we present a detailed physical analysis of the formation of the propagation transverse modes in planar dielectric waveguides using a mathematical-physics approach. We demonstrate physically that, at the wavelength scale, the pure stationary mode inside planar waveguide is described by the cosine function. Meanwhile, the sine function yields a quasi-stationary periodic mode.

Literature about physical sciences has always been scarce in our country,
but even more so before its professionalization among us. For this reason, it
is remarkable the existence of the book Compendio de los fen´omenos de la
Radioactividad y nociones sobre la Constituci´on de la Materia, published in
Mexico City in 1932, in which they were treated with certain amplitude those
subjects, so it turns out to be of some importance to those who investigate
the development of Physics in this nation. This work, written by the engineer
Juan Mateos, was not a translation to Spanish of a book written in another
language elsewhere, but it is an original contribution in our language of its
author, which is relevant, because it shows the early existence of Mexicans
who were aware, at least in general, of the main advances in the research to
establish the nature of matter. In this article, a summary of the material
dealt in this pioneer book is given, because we consider that it sheds light
on the initial efforts to understand matter made in our nation, and to make
known this new field for its research in Physics in our country.

We show that the diagram describing the process to produce mechanical work from the capacitor-batteries system proposed in the reference Rev. Mex. Fís. E 52, 215 (2006) is inconsistent with the analytical results obtained in that paper. Thus, the correct diagram and the process to produce mechanical work are presented.

Several conceptual errors in a recently published paper ({\it Rev.\ Mex.\ F\'{\i}s.\ E} {\bf 64} (2018) 47) dealing with the damped one-dimensional harmonic oscillator are pointed out.

Rev. Mex. Fis. E 65 (2) 2019

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