INSTITUTO DE FISICA LA PLATA
Unidad Ejecutora - UE
congresos y reuniones científicas
Teaching basic special relativity in high school: the role of classical kinematics
ARLEGO MARCELO; OTERO MARIA RITA
Congreso; 2nd World Conference on Physics Education (2nd WCPE); 2016
In this work a possible didactic sequence for the study of basic aspects of special relativity (SR) in high school is presented, resignifying the role of classical kinematics and the Galileo's relativity principle. A first version of the teaching sequence was implemented in Argentina in 2014 and 2015 in four high school courses. Results of those implementations, especially the general proposal and the process of conceptualization are published. The sequence is structured in three phases: The first one refers to the classical (pre‐relativistic) kinematics and the Galileo's relativity principle. Here the motion analysis from different reference systems is proposed, allowing introducing the relativity from the beginning. Thereby, statements like "the car is moving respect to the road" and vice versa acquire the same level of truth and pertinence, conspiring against the idea of a privileged reference frame, deeply rooted in the students. After that, the concept of relative velocity is addressed, based on daily life student?s experience. For instance, a car coming from the opposite lane route approaches us faster than its speedometer indication. This type of situations aims the emergency of the Galileo's law of velocities addition. At the end of the first phase, situations that allow considering the inertia principle and Galilean relativity are presented. To this end it is proposed to personally perform different actions like stay at rest, at uniform motion (respect to the floor), as well as braking, accelerating or moving in a circle, with a pendulum hanging from the hand. With that it is intended that students "experience" the inertia and approach the idea of indistinguishability between rest and uniform translation. This aspect, which is thebasis of the relativity principle, is exploited in the last situation, where it is proposed to infer the state of motion of a wagon (ideally isolated) only with the help of a pendulum hanging from the ceiling. The second part of the sequence consists in a transition to SR, which retakes and generalizes the relativity principle and analyzes the invariance of the light velocity. Here situations related to the simultaneity or non‐simultaneity of events from different reference systems are proposed. In particular, a situation where rubber bullets are fired at the same time, in opposite directions, from the middle of an isolated wagon is presented. In this case, the simultaneous arrival of these bullets at both ends of the wagon is requested to be analyzed from the point of view of a fixed observer inside the wagon and another fixed on the platform, respectively. This analysis requires applying the concepts of relative motion and the relativity principle discussed in the first part. To this end, it is necessary to solve kinematic meeting problems which are treated progressively from a numerical up to a symbolic and graphical level. In the last part of the second phase previous situation but with light is presented. After a discussion about the invariance of the light speed, c the corresponding meeting problem equations are solved by using the technique developed in the first part. Therefore, the non‐ simultaneity phenomenon (for platform observer) emerges, bringing the entrance to the SR. Note that this phase represents a transition because although the result of rubber bullets is (relativistically) incorrect, it enables introducing the issue of simultaneity in a familiar context for students, as well as developing the technique to address the meeting problem for light. The third phase considers basic the kinematical aspects the SR. By using the relativity principle and the c‐invariance, the time dilation, length contraction and the relativistic addition of velocities are considered. The latter allows reconsidering the issue of bullets in a relativistic context, giving to the phenomenon of non‐simultaneity a general character. Finally, situations to address the relativistic aberration, starting from everyday life, low speed, examples are proposed. Currently a new reformulated version of the sequence is being tested in two high school courses of Antioquia (Colombia). The reformulations mainly concern to phases one and two of the sequence. While the aforementioned structure is maintained, the part related to classical kinematics, especially the meeting problems and relative velocity has been extended. Also the use of spreadsheets and graphics software is fomented, which provide versatility and quick access to analyze orders of magnitude and the relevance of c as a natural scale of SR phenomena. In this work some results on the last reformulation of parts one and two are presented.