History of science provides access to a reservoir of meaningful experiments that can be studied and reproduced in classrooms. This is the case of Joule’s paddle-wheel experiment which displays the potentiality to help students improve their understanding of the concept of energy. This experiment has been mentioned in many physics textbooks during the twentieth century. Recently, it has received renewed attention by several researchers in science education. However, the accounts of Joule’s experiment proposed by these researchers are at variance with (...) each other: either in terms of equivalences, in terms of energy change, or in terms of energy transformation and Rankine’s definition. This raises several questions: What is their respective contribution to the understanding of the historical emergence of the energy concept, and to the understanding of the very meaning of this concept? Are these accounts concurrent? Eventually, how can they help for the teaching energy? To investigate these questions, historical details concerning this experiment are first considered. It is stressed that Joule did not made use of the concept of energy, and instead described his experiment in terms of conversion of living force into heat. The three accounts of Joule’s experiment are then presented and their respective contribution discussed. By emphasizing different aspects of this experiment, they are shown to suggest different strategies for teaching energy. For all that, they are not contradictory and, considered together, they bring to light the great potential of Joule’s experiment to foster students understanding of this concept. (shrink)

The concept of energy, the premier concept of physics and indeed of all science, is here investigated from the standpoint of its early historical origin and the philosophical implications thereof. The fundamental assumption is made that the root of the concept is the notion of invariance or constancy in the midst of change. Salient points in the development of this idea are presented from ancient times up to the publication of Lagrange'sMécanique Analytique (1788).

In his Zur Einstein’schen Relativitätstheorie, Ernst Cassirer presents relativity theory as the last manifestation of the tradition of the “physics of principles” that, starting from the nineteenth century, has progressively prevailed over that of the “physics of models.” In particular, according to Cassirer, the relativity principle plays a role similar to the energy principle in previous physics. In this article, I argue that this comparison represents the core of Cassirer’s neo-Kantian interpretation of relativity. Cassirer pointed out that before and after (...) Kant, the history of physics presents significant instances in which the search for formal conditions that the laws of nature must satisfy preceded and made possible the direct search for such laws. In his earlier years, Cassirer seems to have regarded principles like the energy principle, the relativity principle, and the principle of least action as a constitutive but provisional form of a priori, imposing specific limitations on the form of the allowable laws of nature. Only in his later years, by attributing an autonomous status to these statements of principle, did Cassirer attribute a definitive but merely regulative meaning to the a priori. This does not impose specific requirements on natural laws but only a motivation to search for them. (shrink)