[en] In this paper we propose a mathematical model to describe a theoretical device able to simulate an inverse-square force on a test mass moving on a horizontal plane. We use two pulleys, a counterweight, a wire and a smooth rail, in addition to the test mass. The tension of the wire (i.e. the attractive force on the test mass) is determined by the position of a counterweight free to move on a rail placed under the plane. The profile of the rail is calculated in order to obtain the required Newtonian force. Details of this calculation are reported in the paper, and numerical simulations are provided in order to investigate the stability of the orbits under the effect of the main friction forces and other perturbative effects. This work points out that there are some criticalities intrinsic to the apparatus and gives some suggestions about how to minimize their impact. (paper)

[en] Endoreversible thermodynamics is a theory for the description of irreversible thermodynamic processes. In this theory a non-equilibrium system is divided into a set of reversible subsystems which interact irreversibly with one another by exchanging energy and extensive quantities. These extensities act as carriers for the energy. ETA-Graphics is a graphics-based interface to endoreversible thermodynamics that can be used as an educational aid. It enables students to visually design endoreversible systems by drawing reversible subsystems and connecting them with irreversible (or reversible) interactions. Through special dialogs users specify the properties of the system, e.g., in form of transport laws for energy and extensive quantities. Based on the input ETA-Graphics allows students to analyse the endoreversible systems and their properties. Therefore, performance measures, i.e., efficiency and total power output, are calculated. Additionally, graphical representations of the results are shown. (paper)

[en] Radiation transfer is an important topic in several physical disciplines, probably most prominently in astrophysics. Computer scientists use radiation transfer, among other things, for the visualization of complex data sets with direct volume rendering. In this article, I point out the connection between physical radiation transfer and volume rendering, and I describe an implementation of direct volume rendering in the astrophysical radiation transfer code RADMC-3D. I show examples for the use of this module on analytical models and simulation data. (paper)

[en] Contemporary physicists and science experts include Eratosthenes’ measurement of the Earth's circumference as one of the most beautiful experiments ever performed in physics. Upon revisiting this famous event in the history of science, we find that some interesting generalizations are possible. On the basis of a rather simple model of the Earth's insolation, we have managed, using some advanced mathematics, to derive a new formula for determining the length of the year, generalized in such a way that it can be used for all planets with sufficiently small eccentricity of the orbit and for all locations with daily sunrises and sunsets. The practical technique that our formula offers is simple to perform, entirely Eratosthenian in spirit, and only requires the angle of the noonday sun to be found on successive days around an equinox. Our results show that this kind of approach to the problem of the Earth's insolation deserves to be included in university courses, especially those which cover astronomy and environmental physics. (paper)

[en] Once a controversial idea, the fact that gases like air have weight can easily be demonstrated using reasonably precise scales in the modern teaching laboratory. But unlike a liquid, where a mechanical model suggests a pile of hard spheres resting on each other, gas molecules are in continual motion and can have minimal interaction. How should we think about the effect these molecules have on the scale? And more importantly, how should we explain it to students? Several models of gas behavior are employed to answer these questions and it is shown how the weight of a gas is, like electric current, an emergent phenomena in contrast to the weight of a liquid which is direct or causal. (paper)

[en] We address the problem of constructing a network of unit resistors such that it enables the retrieval of an arbitrary value of equivalent resistance. In particular, we employ the notion of continued fractions to construct a ladder network by which we can easily obtain any fractional value resistance. In addition, since any irrational number is associated with an infinite continued fraction, we discuss the convergence of the equivalent resistance of an infinite resistive ladder and various aspects concerning the approximations of arbitrary numbers attained by adding additional resistors successively to the network. The presented methods can be easily implemented in an educational laboratory and offer an interesting addition to the topic of Ohm’s law. (paper)

[en] Exponential decay is a prototypical functional behaviour for many physical phenomena, and therefore it deserves great attention in physics courses at an academic level. The absorption of the electromagnetic radiation that propagates in a dissipative medium provides an example of the decay of light intensity, as stated by the law of Lambert–Beer–Bourguer. We devised a very simple experiment to check this law. The experimental setup, its realization, and the data analysis of the experiment are definitely simple. Our main goal was to create an experiment that is accessible to all students, including those in their first year of academic courses and those with poorly equipped laboratories. As illustrated in this paper, our proposal allowed us to develop a deep discussion about some general mathematical and numerical features of exponential decay. Furthermore, the special setup of the absorbing medium (sliced in finite thickness slabs) and the experimental outcomes allow students to understand the transition from the discrete to the continuum approach in experimental physics. (papers)

[en] Despite the fact that it has been known since the time of Heisenberg that quantum operators obey a quantum version of Newton's laws, students are often told that derivations of quantum mechanics must necessarily follow from the Hamiltonian or Lagrangian formulations of mechanics. Here, we first derive the existing Heisenberg equations of motion from Newton's laws and the uncertainty principle using only the equations F=((dP)/(dt)), P=m((dV)/(dt)), and [X, P] = i. Then, a new expression for the propagator is derived that makes a connection between time evolution in quantum mechanics and the motion of a classical particle under Newton's laws. The propagator is solved for three cases where an exact solution is possible: (1) the free particle; (2) the harmonic oscillator; and (3) a constant force, or linear potential in the standard interpretation. We then show that for a general for a general force F(X), by Taylor expanding X(t) in time, we can use this methodology to reproduce the Feynman path integral formula for the propagator. Such a picture may be useful for students as they make the transition from classical to quantum mechanics and help solidify the equivalence of the Hamiltonian, Lagrangian, and Newtonian pictures of physics in their minds. (paper)

[en] The Peierls argument is a mathematically rigorous and intuitive method to show the presence of a non-vanishing spontaneous magnetization in some lattice models. This argument is typically explained for the D = 2 Ising model in a way which cannot be easily generalized to higher dimensions. The aim of this paper is to present an elementary discussion of the Peierls argument for the general D-dimensional Ising model. (paper)

[en] This paper addresses a small power demonstration unit that has been designed, built and tested to carry out heat transfer studies on the performance of heat pipes embedded in laptops. The main components of the unit are a heat pipe taken from a commercial laptop, a power resistor, a small fan and proper instrumentation. Results from a number of experiments involving realistic combinations of heat power and airflow rates are presented. A detailed thermal analysis is carried out in order to estimate the airflow convective heat transfer coefficient through the condensation section of the heat pipe using the Wilson plot method. Laboratory practices with the demonstration unit seek to solidify students’ understanding of convection heat transfer and also demonstrate real-world applications where heat transfer plays a key role. (paper)