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Rodrigo de Abreu

Publications and source records attributed to Rodrigo de Abreu.

18 recordsLinked to original sources
arXiv2012

The concepts of work and heat and the first and second laws of thermodynamics

A simple and effective approach to thermodynamics is suggested, which solves the major difficulties in the traditional presentation of the subject. The internal energy is introduced from the behavior of deformable bodies, whereas the importance of keeping in mind the microscopic picture is emphasized. A straightforward model is used to show that the internal energy depends on the volume and entropy, from where the relationship between mechanics and thermodynamics is immediate, mechanics corresponding to isentropic thermodynamics. The questions of evolution to equilibrium and irreversibility are studied under the light of the action of the "dynamic force", which has a dissipative character. The present formulation leads to a discussion and clarification of the physical meaning of various thermodynamic quantities, such as pressure, temperature, work and heat. The adiabatic piston problem is analyzed, as a paradigmatic case where the notions of "adiabatic" and "heat transfer" are often ill-defined.

physics.gen-ph↗
arXiv2010

Comment on 'A close examination of the motion of an adiabatic piston' by Eric A. Gislason [Am. J. Phys. 78, 995-1001 (2010)]

A recent paper by Gislason published in Am. J. Phys. deals with the celebrated example of the so-called "adiabatic piston", a system involving two ideal gases contained in a horizontal cylinder and separated by an insulating piston that moves without friction. While the analysis presented in that paper is rather comprehensive, very interesting and useful as a teaching tool, it can be somewhat misleading if not taken within its appropriate context. As a matter of fact, the evolution to equilibrium involves two phases, a faster one leading to the equalization of pressures, and a slower one bringing the system to identical temperatures. Although Gislason addresses only the first process, we note that the final state after the second phase, the evolution to equal temperatures once the pressures are the same, is described by thermodynamics. Therefore, the discussion of the adiabatic piston given by Gislason can and should be enriched, in order to promote a proper and general view of thermodynamics.

physics.class-ph↗
arXiv2009

Comment on 'A one-way speed of light experiment'

A recent paper published in Am. J. Phys. describes an experiment designed to measure the one-way speed of light. Although the experiment is very interesting, in particular to be used in student laboratories, it is in fact determining the two-way speed of light.

physics.gen-ph↗
arXiv2006

Special Relativity in Absolute Space: from a contradiction in terms to an obviousness

This work deals with the questions of absolute space and relativity. In particular, an alternative derivation of the effects described by special relativity is provided, which is based on a description that assumes a privileged reference frame. The present theory follows the ideas of Lorentz and Poincare, abandoning a strict view of Einstein's "equivalence" of all inertial frames. The meaning of the Principle of Relativity is discussed and elucidated, and it is shown that it is not incompatible with the existence of a preferred, absolute, frame. Most scientists nowadays still consider the basic assumptions of the theory proposed here to be plain wrong. Moreover, they tend to see an irreconcilable conflict between the Lorentz-Poincare and the Einstein-Minkowski formulations. However, as stated by John Bell [Bell1988], although there is a stringent "difference in philosophy" between both views, "the facts of physics do not oblige us to accept one philosophy rather than the other". The validity of Bell's assertion is unambiguously demonstrated, and it is shown how and why both approaches do indeed agree in the description of (most of?) the physical phenomena. Evidently, the physical meaning of the different physical quantities - such as "time", "speed", "simultaneity" and "synchronization" - is quite different in both programmes. And yet, for perplexing it may look at first sight, the present theory, developed under the Lorentz-Poincare assumption of a preferred reference frame, somehow encompasses Einstein's theory. There is no conflict, as there is one theory. It is stressed that reality is not changed by the choices one makes to describe it, so it is not changed by the particular way in which the clocks have been set.

physics.ed-ph↗
arXiv2005

Is the assumption of a special system of reference consistent with Special Relativity?

In a previous work we have shown that the null result of the Michelson-Morley experiment in vacuum is deeply connected with the notion of time. The same is true for the the postulate of constancy of the two-way speed of light in vacuum in all frames independently of the state of motion of the emitting body. The argumentation formerly given is very general and has to be true not only within Special Relativity and its `equivalence' of all inertial frames, but as well as in Lorentz-Poincaré scenario of a preferred reference frame. This paper is the second of a trilogy intending to revisit the foundations of Special Relativity, and addresses the question of the constancy of the one-way speed of light and of the differences and similarities between both scenarios. Although they manifestly differ in philosophy, it is debated why and how the assumption of a "special system of reference experimentally inaccessible" is indeed compatible with Einstein's Special Relativity, as beautifully outlined and discussed by John Bell [1]. This rather trivial statement is still astonishing nowadays to a big majority of scientists. The purpose of this work is to bring such assertion into perspective, widening the somewhat narrow view of Special Relativity often presented in textbooks.

physics.ed-ph↗
arXiv2005

The conceptualization of time and the constancy of the speed of light

In this work we show that the null result of the Michelson-Morley experiment in vacuum is deeply connected with the notion of time. It can be deduced without any mathematics only from the assumption that all good clocks can be used to measure time with the same results, independently of the machinery involved in their manufacturing. A second important assumption, intrinsic to the very notion of time, is that clocks measure time in the same way in different frames, i.e., the notion of time is the same in all inertial frames. Under this assumption, we point out that the "postulate" of constancy of the "two-way" speed of light in vacuum in all frames independently of the state of motion of the emitting body is also strongly related to the concept of time, together with the existence of a limit speed in the "rest frame". This postulate simply results from the construction of clocks where tic-tacs are made by objects traveling with the limit speed.

physics.ed-ph↗
arXiv2002

Estabelecimento do Conceito de Temperatura como uma grandeza derivada da Energia e da Entropia

Temperature is introduced as a derived concept from energy and entropy. We consider two sub-systems in equilibrium for several configurations. The equality of temperature of the sub-systems is obtained from the equilibrium condition. The isothermal transformation is defined for several configurations and from this definition we obtain the Clausius-Clapeyron equation. We apply the analysis to the ideal gas. The classical ideal gas appears as a limit and the problem of the measurement of temperature is analysed.

physics.gen-ph↗
arXiv2002

The physical meaning of synchronization and simultaneity in Special Relativity

Based on two previous papers, the physical meaning of synchronization and simultaneity as is presented in Einstein's Special Relativity paper of 1905 is reconsidered. We follow Einstein's argumentation to introduce a criterium of synchronization and for the same arguments we arrive at a different criterium for synchronization. From that we conclude that simultaneity is absolute.

physics.gen-ph↗
arXiv2002

Analise Termodinamica da aceleracao de uma massa

We analyse the acceleration of a mass with a simple structure taking into account Thermodynamics. Two situations are analysed. The first one for the application of a localized force to a point of the mass. The second one for the application of a force to the entire mass. The two situations are not equivalent. For the first situation we have an increase of temperature of the mass, resulting from an internal damping, during a transient.

physics.gen-ph↗
arXiv2002

A Segunda Lei da Termodinamica na formulacao da Lei de Hooke

Hooke's Law is analyzed taking the Second Law of Thermodynamics into consideration. It is shown that the energy of a spring isn't always 1/2 k xx - this value is actually the energy of the spring plus the energy of the atmosphere that surrounds it. On a quasi-isentropic aproximation in which the dynamic force is approximately the same as the static force, k is not a constant. Only by considering an ideal spring where k is constant and only on a static regime, can we say the energy is 1/2 k xx. For any dynamic regime of such an ideal spring, the energy of the spring is a function of its temperature and therefore is different from 1/2 k xx. If any given mass is moving attached to an ideal spring, the movement will eventually cease even if such movement occurs in vacuum. The dynamic force is not the static force kx. The Second Law of Thermodynamics is essential in order to formulate Hooke's Law.

physics.gen-ph↗
arXiv2002

Deduction of Lorentz Transformation from the existence of absolute rest. Deduction of the speed of light in any frame of reference

We begin by admitting the following: (i) there is a frame of reference where the speed of light is the same in any direction (that speed is c) (ii) the average speed of light on a two-way journey is c in every frame of reference. From this two premises we obtain an expression for the speed of light which implies the speed of light depends on the motion of the frame of reference. Also from this two premises solely we deduct Lorentz Transformation.

physics.gen-ph↗
arXiv2002

A relativistic time variation of matter/space fits both local and cosmic data

Cosmic observations strongly support a time varying scenario for matter/space. On the other hand, so far, observations at solar system scale failed to identify any time variation on matter/space characteristics. To explain both results it is enough to consider a time variation of physical parameters liable to account for cosmic observations but satisfying Relativity Principle at least at local scale (we called it Local Relativity Property). Here, for the first time, a relativistic time varying scenario is defined from redshift and Cosmic Microwave Background characteristics. It is showed that it can match both cosmic and local data. Although undetectable in each local measure, such relativistic scenario has detectable time dependent consequences at Solar System scale, namely a receding component in the motion of the Moon, a past warmer climate and, this being new, an accelerating component in Earth rotation. A new class of cosmological models can now be explored, without concepts like dark matter, valid at both local and cosmic scale, and such that fundamental physical laws and Relativity Principle hold in any point of time and space.

astro-ph↗
arXiv2002

The Energy-Entropy Principle

In this paper, through a criticism of what we call the paradigmatic view of thermodynamics, we aim at showing a new perspective attained in this matter. The generalization of heat as internal energy (generalization of the kinetic energy concept of heat) permits the generalization of the Kelvin postulate: "It is impossible, without another effect, to convert internal energy into work" (no reference to heat or to heat reservoir).

physics.gen-ph↗
arXiv2002

The First Principle of Thermodynamics and the Non-Separability of the Quantities "Work" and "Heat": The adiabatic piston controversy

The impossibility of separating into work and heat the energy transmitted between two subsystems through a movable piston is analyzed in this article. The process here described, although "quasi-static", is not reversible. It is shown that the First Principle, dU=dW+dQ, introduced by Clausius, does not generally allow a physical identification of dW and dQ, although dU=-pdV+TdS is verified along the equilibrium points of each subsystem.

cond-mat.stat-mech↗
arXiv2002

Cosmological Principle and Relativity - Part I

The absence of an identified consequence at solar system scale of the cosmological space expansion is usually explained considering that space expansion does not affect local anysotropies in matter distribution. This can also be explained considering a time dependent scenario compatible with Relativity Principle, therefore supporting physical laws independent of the time position of the observer. A theory considering such relativist scenario, i.e., generalizing Relativity Principle to position, embodies Cosmological Principle and can be intrinsically able to fit directly both local and cosmic data. In part I it is presented the general framework of such a theory, called Local Relativity (LR), and analysed the space-time structure. Special Relativity space-time is obtained, with no formal conflict with Einstein analysis, but fully solving apparent paradoxes and conceptual difficulties, including the simultaneity concept and the long discussed Sagnac effect. In part II, LR is applied to positional analysis. It is verified the accordance with solar system measurements and with classic cosmic tests, without dark matter or dark energy. Two of the new features obtained in part II are the possibility of a planetary orbital evolution compatible with a null determination for G variation, supporting a warmer scenario for earth (and Mars) past climate, and the possibility of an accelerating component in earth rotation, compatible with the most recent measurements.

physics.gen-ph↗
arXiv2002

Reinterpretation of Lorentz Transformation and resolution of Special Relativity's paradoxes

Lorentz Transformation is reinterpreted. It is shown that by admitting the existence of a frame of reference with synchronized clocks, we conclude that any other frame of reference that moves related to the first has desynchronized clocks. From this conclusion we will arrive at a new expression to relate the time of different frames of reference. We also arrive at a new expression to relate the contraction of different frames. We will show that if the maximum speed on a frame with synchronized clocks is the speed of light, then the speed of light varies accordingly to the velocity of the frame of reference. The new interpretation of Lorentz Transformation explains and solves Relativity's paradoxes.

physics.gen-ph↗