La física de la fuerza impresa y sus implicaciones para la enseñanza de la mecánica

When exarnining learners' understanding of questions involving the movement of projectiles one notices, in general, that their common sense is far away from making any reference to aristotelian antiperistasis. The causes for a 'violent' or forced movement are seen as located in the body itself, following from the projectile-projector interaction. This is essentially the concept of impressed force, introduced by astronomer Hipparcus (second century BC) and adopted by Philoponus (sixth century), among others. The notion of impressed force has an interesting historical development.It may have been a reference for the establishment of the impetus theory by Buridan in the fourteenth century, and was part of the debate that took place from the twelfth century onwards about the possible movement of a projectile in the void. This work explores historically this concept, making use of it in problem situations that are both well familiar to the students and relevant for the development of mechanics. From the point of view of teaching that takes into consideration the learners' ideas, this theme has great didactic potential for the development of strategies to help the reformulation of their conceptions, turning them more consistent with what is accepted as scientific today

Mechanics, cosmology and Mach's principle

It is pointed out that recent cosmological findings seem to support the view that the mass/energy distribution of the universe defines the Newtonian inertial frames as originally suggested by Mach. The background concepts of inertial frame, Newton's second law, and fictitious forces are clarified. A precise definition of Mach's principle is suggested. Then an approximation to general relativity discovered by Einstein, Infeld, and Hoffmann is used and it is found that this precise formulation of Mach's principle is realized provided the mass/energy density of the universe has a specific value. This value turns out to be twice the critical density. The implications of this approximate result is put into context.Comment: 9 pages, 34 references, 0 figure

The role of empirical research in the study of complex forms of governance in agroindustrial systems

The growing complexity of supply chains poses new challenges for Agricultural Research Centers and statistical agencies. The aim of this perspective paper is to discuss the role of empirical research in understanding the complex forms of governance in agribusiness. The authors argue that there are three fundamental levels of analysis: (i) the basic structure of the market, (ii) the formal contractual arrangements that govern relations within the agroindustrial system and (iii) the transactional dimensions governed by non-contractual means. The case of the agrochemical industry in Brazil illustrates how traditional analyses that only address market structure are insufficient to fully explain the agricultural sector and its supply chain. The article concludes by suggesting some indicators which could be collected by statistical agencies to improve understanding of the complex relationships among agribusiness segments. In doing so, the paper seeks to minimize costs and to enable a better formulation of public and private policies

How might educational research into children’s ideas about light be of use to teachers?

This paper offers a synthesis of research evidence around teaching light to primary and secondary school pupils, as part of the Institute of Physics (IOP) Promoting and Interpreting Physics Education Research (PIPER) project. Conceptual change literature describes many difficulties young people have with understanding the phenomenon of light, and this knowledge can be useful in the classroom. Pupil teacher dialogue is used to illustrate some of the pedagogical challenges teachers face in this topic. This paper highlights a range of influences on pupils from everyday life and from the classroom, with a view to promoting teacher awareness of conceptual change research evidence