Xavier Jaén

Rigid motions and generalized Newtonian gravitation

In an effort to contribute to a better understanding of General Relativity, here we lay the foundations of generalized Newtonian gravity, which unifies inertial forces and gravitational fields. We also formulate a kind of equivalence principle for this generalized Newtonian theory. Finally, we prove that the theory we propose here can be obtained as the non-relativistic limit of General Relativity.

Homothetic motions and Newtonian cosmology

We construct a homothetic covariant Newtonian gravitation theory which unifies inertial homothetic forces and gravitational fields. This is achieved through an equivalence principle based on a local homothetic frame of motion. As a consequence, we can obtain a coherent Newtonian cosmology which admits a cosmological principle and leads to the Friedman equations for a dust universe. Finally we prove that this gravity theory can be obtained as the non-relativistic limit of a class of metrics in General Relativity. The Friedmann–Lemaitre–Robertson–Walker metric and its limit are also studied.We construct a homothetic covariant Newtonian gravitation theory which unifies inertial homothetic forces and gravitational fields. This is achieved through an equivalence principle based on a local homothetic frame of motion. As a consequence, we can obtain a coherent Newtonian cosmology which admits a cosmological principle and leads to the Friedman equations for a dust universe. Finally we prove that this gravity theory can be obtained as the non-relativistic limit of a class of metrics in General Relativity. The Friedmann–Lemaître–Robertson–Walker metric and its limit are also studied.

Semi-virtual lectures on physics

Some years ago, it was believed that the learning process would eventually become mostly virtual. ICT tools were therefore designed with this scenario in mind. Nevertheless, todays learning process is still predominantly face-to-face; at most, we have seen a shift towards blended learning. Today we are in the process of incorporating ICT tools both inside and outside of the classroom. In this paper, we explore how contents—specifically physics contents—can be used optimally either inside or outside of the classroom.

Teaching and Learning Physics Using the Internet: The Baldufa Project

The aim of the Baldufa project that is presented in this article is to help both teachers and students in teaching‐learning activities in physics. A certain amount of HTML documentation is available, at this moment, to be used by students as learning aids. Teachers can propose their own pedagogical strategies via the Internet. For these reasons, the authors have programmed a server and have conceived a teaching package in HTML language.

Rigid covariance as a natural extension of Painleve-Gullstrand space-times: gravitational waves

The group of rigid motions is considered to guide the search for a natural system of space-time coordinates in General Relativity. This search leads us to a natural extension of the space-times that support Painlevé–Gullstrand synchronization. As an interesting example, here we describe a system of rigid coordinates for the cross mode of gravitational linear plane waves.The group of rigid motions is considered to guide the search for a natural system of space-time coordinates in General Relativity. This search leads us to a natural extension of the space-times that support Painleve–Gullstrand synchronization. As an interesting example, here we describe a system of rigid coordinates for the cross mode of gravitational linear plane waves.

On the meaning of Painlevé–Gullstrand synchronization

Following on from two recent papers, here we examine the relationship between Newtonian gravitation and general relativity in more depth. This allows us to define a scalar potential which is just the proper time of the vector potential when the latter is interpreted as the geodesic velocity field. The results are closely related to spacetimes that admit Painlevé–Gullstrand synchronization.

Comparative study of three audio processors as environments for laboratory activities on wave physics and acoustics

Audio processors allow to implement laboratory activities specially on acoustics. We have evaluated three audio processors (Audacity, WaveLab, and Adobe Audition). Although an overall grade was also calculated as a guideline (not a statement of “the best”), the decision about the most suitable one depends on each particular laboratory activity.

Description and evaluation of a hybrid basic optics course

In this paper, the authors present and evaluate a partially web‐based Basic Optics course held each year from 2000 to 2003. The course has evolved over the last four years, and we analyse this process based on students’ responses to a paper‐based questionnaire. Their responses show the difficulty they had in adapting to this new environment, in which they are required to actively participate in their learning process. One positive aspect that has been brought to our attention as teachers is that it is necessary to reflect on the learning model we would like to introduce. In other words, the focus has shifted from the course contents to designing effective teaching and learning processes.

Rigid covariance, equivalence principle and Fermi rigid coordinates: gravitational waves

For a given space-time and for an arbitrary time-like geodesic, we analyze the conditions for the construction of Fermi coordinates so that they are also rigid covariant. We then apply these conditions to linear plane gravitational waves.

Virtual Information Managers in Physics Education Context

In this article, the authors analyze how educational institutions behave in relation with the contents available through the web. They also reflect on the features of the currently available information managers (IMs), from an educational point of view. They found there is a lack of tools for information management at low scale when it has to be used as a resource for teaching and learning. Finally, they propose a solution, which consists of naming a “small virtual educational library” (SVEL), and they show how it works in a physics education context.