1,721,006 research outputs found
Du frottement à la tribologie : survol historique.
No full textThe article proposes a short history of the research on friction. For every period, the most important themes and results are outlined: the early laws and theories on friction from Leonardo to Amontons and Coulomb; the theory of lubrication and the models of rolling friction, from 1840 to 1930; the theories of wear, the synthesis of Bowden and Tabor and the birth of tribology; the recent developments, with the new scientific instruments and the study of friction at the atomic scale, the nanotribology. Some didactic reflections introduce and conclude the article
Students' conceptions of fluids
No full textThis article describes a research study concerning students’ conceptions and reasonings about fluids and pressure in static situations. After a preliminary survey involving interviews and observations in class, some written questions were answered by various groups, totalling 428 Italian and French pupils in upper secondary school, 458 first-year university students in Belgium and 58 teachers-in-training. After briefly illustrating some results
from previous research on this topic, the article introduces the guidelines and objectives of the current research, describes and discusses its results, highlighting some categories of the more diffuse conceptions and tendencies of reasoning, and supplies a few suggestions for teaching. It is shown, among other things, that the notion of hydrostatic pressure is strongly connected to the idea of weight and associated with all the ambiguities that
usually go with the latter. Moreover, a critical point appears to be the difficulty in connecting local actions and global effects, the need for systemic reasonings that are capable of producing the mechanism with which to establish a situation of equilibrium
The history of cooling law: when the search for simplicity can be an obstacle
No full textThis paper presents an historical overview of the research on the cooling law, from Newton until the beginning of 20th century, and provides some suggestions for the use of this history as a resource for teaching. This history begins with a description and an interpretation of Newton’s earlier works in 1701 and an overview of studies confirming or confuting Newton’s law during the 18th century. Subsequently, it presents the early studies on cooling due to radiant heat, the fundamental work of Dulong & Petit published in 1817, and a brief overview of the research conducted after 1850 on the laws of thermal radiation and of natural and forced convection. It is shown that many scientists persisted in maintaining Newton’s law, despite numerous evidence to the contrary, by attributing the found discrepancies to empirical errors or to other disturbance factors. Many scientists considered this law as a fundamental principle rather than a conjecture to be tested by means of experiments, while others were searching for a different but general and unique cooling law. The faith in the simplicity of natural laws and the spontaneous idea of proportionality between cause and effect seem to have strongly influenced Newton and many later scientists. A discussion of epistemological, methodological and pedagogical implications is offered
Work and Energy in the Presence of Friction: The Need for a Mesoscopic Analysis
No full textThis paper deals with some of the difficulties involved in correctly linking the mechanical and thermodynamic descriptions of situations where there are bodies in motion and changes in temperature and/or heat exchanges. It proposes and discusses a definition of internal energy and shows that the total work of the non-conservative forces, such as frictional forces, always equals zero. The energy balances of two bodies in motion in the presence of sliding friction are analysed in this way; the calculation of the work of frictional forces is discussed, taking into account the mesoscopic level
Do things weigh more or less in the mountains?
No full textThe notion of weight can be associated with three distinct physical quantities: the force of gravity due to the Earth; the resultant of this gravitational force and the centrifugal force arising from the Earth’s rotation; and the ‘apparent weight in air’, i.e., what is measured by a scale located in the Earth’s atmosphere. Starting from a real life student–teacher exchange, this article sets out the variety of meanings that students and teachers may attribute to the term ‘weight’. It then explores how the weight and apparent weight of an object vary with mountain altitude. The effects of the mass of the mountain and the buoyant force of the air are considered and calculated. The question of whether apparent weight increases or decreases with increasing elevation
is addressed in detail
Le mésoscopique en physique et en didactique
No full textL’importance et le pouvoir explicatif des modèles microscopiques représentant atomes et/ou molécules sont bien reconnus. Toutefois, dans de nombreuses situations, une description à une échelle intermédiaire, mésoscopique, devient utile et nécessaire.
Récemment, le rôle de cet aspect dans l’enseignement a été étudié et souligné par des recherches didactiques. Cet article veut montrer combien l’utilisation d’une échelle intermédiaire
est répandue et importante en physique. Il donne plusieurs exemples relatifs à différents secteurs de la physique, ainsi que des précisions terminologiques. Ensuite, il analyse plus en détail certaines situations critiques, dans lesquelles l’approche mésoscopique devient essentielle pour une bonne compréhension et pour éviter erreurs et contradictions : la distinction entre travail et chaleur, le frottement solide, le passage d’une description discontinue à une continue. Il conclut en prônant une plus grande attention à ces aspects dans l’enseignement
Da Leonardo da Vinci alla nanotribologia: storia delle ricerche e delle teorie sui fenomeni d'attrito. Prima parte: Le leggi dell'attrito radente, le teorie della lubrificazione e gli studi sull'attrito volvente.
No full textThe paper present an overview of the history of scientific research concerning friction, lubrication and wear. The most important topics and results of research on friction, from antiquity to now, are outlined. This first part of the work (the second one was published in the next issue of this journal), concerns the period from antiquity to1930: the early laws and theories, from Leonardo to Amontons and Coulomb; the theory of lubrication and the models of rolling friction from 1840 to 1930. Didactic observations and suggestions introduce and conclude the paper
Le principe de Pascal pour les fluides n’est pas toujours vrai
No full textCet article présente une analyse du principe de Pascal pour les fluides. Je distingue une version faible et une version forte du principe, et je montre qu’en présence d’un champ externe le principe n’est pas généralement valable. Quelques exemples impliquant
des liquides et des gaz sont développés et des données numériques sont fournies
Da Leonardo da Vinci alla nanotribologia: storia delle ricerche e delle teorie sui fenomeni d'attrito. Seconda parte: Le teorie dell'usura, la sintesi di Bowden e Tabor, l'attrito a livello atomico.
No full textThe paper present an overview of the history of scientific research concerning friction, lubrication and wear. The most important topics and results of research on friction, from antiquity to now, are outlined. This second part of the work (the first one was published in the previous issue of this journal), concerns the period from 1930 to now: the theories of wear, the synthesis of Bowden and Tabor and the birth of tribology, the more recent developments, friction at the nano-scale and nanotribology. Didactic observations and suggestions introduce and conclude the paper
The distinction between heat and work: an approach based on a classical mechanical model
No full textThe distinction between work and heat is obvious in most typical situations, but becomes difficult in certain critical cases. The subject is discussed in texts on thermodynamics and has long given rise to debate. This paper presents an approach based on a mesoscopic analysis, using a simple mechanical model, in which bodies are made up of particles (representing atoms and/or molecules) treated as material points interacting with forces that obey Newton's laws. The sum of the work done by these microscopic forces is split into two terms representing the macroscopic quantities work and heat
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