Paolo Mascheretti

How to teach friction: Experiments and models

Students generally have difficulty understanding friction and its associated phenomena. High school and introductory college-level physics courses usually do not give the topic the attention it deserves. We have designed a sequence for teaching about friction between solids based on a didactic reconstruction of the relevant physics, as well as research findings about student conceptions. The sequence begins with demonstrations that illustrate different types of friction. Experiments are subsequently performed to motivate students to obtain quantitative relations in the form of phenomenological laws. To help students understand the mechanisms producing friction, models illustrating the processes taking place on the surface of bodies in contact are proposed.

Studying the physical basis of global warming: thermal effects of the interaction between radiation and matter and greenhouse effect

We present a teaching module dealing with the thermal effects of interaction between radiation and matter, the infrared emission of bodies and the greenhouse effect devoted to university level and teacher education. The module stresses the dependence of the optical properties of materials (transparency, absorptivity and emissivity) on radiation frequency, as a result of interaction between matter and radiation. Multiple experiences are suggested to favour a progressive construction of knowledge on the physical aspects necessary to understand the greenhouse effect and global warming. Some results obtained with university students are briefly reported.

A Three‐Dimensional Approach and Open Source Structure for the Design and Experimentation of Teaching‐Learning Sequences: The case of friction

We have developed a teaching‐learning sequence (TLS) on friction based on a preliminary study involving three dimensions: an analysis of didactic research on the topic, an overview of usual approaches, and a critical analysis of the subject, considered also in its historical development. We found that mostly the usual presentations do not take into account the complexity of friction as it emerges from scientific research, may reinforce some inaccurate students’ conceptions, and favour a limited vision of friction phenomena. The TLS we propose begins by considering a wide range of friction phenomena to favour an initial motivation and a broader view of the topic and then develops a path of interrelated observations, experiments, and theoretical aspects. It proposes the use of structural models, involving visual representations and stimulating intuition, aimed at helping students build mental models of friction mechanisms. To facilitate the reproducibility in school contexts, the sequence is designed as an open source structure, with a core of contents, conceptual correlations and methodological choices, and a cloud of elements that can be re‐designed by teachers. The sequence has been tested in teacher education and in upper secondary school, and has shown positive results in overcoming student difficulties and stimulating richer reasoning based on the structural models we suggested. The proposed path has modified the teachers’ view of the topic, producing a motivation to change their traditional presentations. The open structure of the sequence has facilitated its implementation by teachers in school in coherence with the rationale of the proposal.

Computer Simulation and Laboratory Work in the Teaching of Mechanics

By analysing the measures of student success in learning the fundamentals of physics in conjunction with the research reported in the literature one can conclude that it is difficult or undergraduates as well as high-school students to gain a reasonable understanding of elementary mechanics. Considerable effort has been devoted to identifying those factors which might prevent mechanics being successfully learnt and also to developing instructional methods which could improve its teaching (Champagne et al. 1984, Hewson 1985, McDermott 1983, Saltiel and Malgrange 1980, Whitaker 1983, White 1983). Starting from these research results and drawing from their own experience (Borghi et al. 1984, 1985), they arrived at the following conclusions. A strategy based on experimental activity, performed by the students themselves, together with a proper use of computer simulations, could well improve the learning of mechanics and enhance the interest in, and understanding of, topics which are difficult to treat in a traditional way. The authors describe the strategy they have designed to help high school students to learn mechanics and report how they have applied this strategy to their particular topic of projectile motion.

Investigating the role of sliding friction in rolling motion: a teaching sequence based on experiments and simulations

We designed a teaching–learning sequence on rolling motion, rooted in previous research about student conceptions, and proposing an educational reconstruction strongly centred on the role of friction in different cases of rolling. A series of experiments based on video analysis is used to highlight selected key concepts and to motivate students in their exploration of the topic; and interactive simulations, which can be modified on the fly by students to model different physical situations, are used to stimulate autonomous investigation in enquiry activities. The activity sequence was designed for students on introductory physics courses and was tested with a group of student teachers. Comparisons between pre- and post-tests, and between our results and those reported in the literature, indicate that students’ understanding of rolling motion improved markedly and some typical difficulties were overcome.

Microscopic models for bridging electrostatics and currents

A teaching sequence based on the use of microscopic models to link electrostatic phenomena with direct currents is presented. The sequence, devised for high school students, was designed after initial work carried out with student teachers attending a school of specialization for teaching physics at high school, at the University of Pavia. The results obtained with them are briefly presented, because they directed our steps for the development of the teaching sequence. For both the design of the experiments and their interpretation, we drew inspiration from the original works of Alessandro Volta; in addition, a structural model based on the particular role of electrons as elementary charges both in electrostatic phenomena and in currents was proposed. The teaching sequence starts from experiments on charging objects by rubbing and by induction, and engages students in constructing microscopic models to interpret their observations. By using these models and by closely examining the ideas of tension and capacitance, the students acknowledge that a charging (or discharging) process is due to the motion of electrons that, albeit for short time intervals, represent a current. Finally, they are made to see that the same happens in transients of direct current circuits.

Investigating the magnetic interaction with Geomag and Tracker Video Analysis: static equilibrium and anharmonic dynamics

In this paper, we describe how simple experiments realizable by using easily found and low-cost materials allow students to explore quantitatively the magnetic interaction thanks to the help of an Open Source Physics tool, the Tracker Video Analysis software. The static equilibrium of a ‘column’ of permanents magnets is carefully investigated by working on digital photos, while the anharmonic oscillations of a magnetic bar under the action of gravity and of magnetic repulsion are analysed by using a digital video. A detailed comparison between theoretical expectations and experimental results is discussed. We discuss how the magnetic force falls off with the distance between the permanent magnets following an inverse pth power law. Static and dynamic measurements of the force and of the periods for small amplitude harmonic oscillations yield an experimental value for p ≈ 2. The dynamical system is a good example of an anharmonic oscillator. The experiments need simple and inexpensive material to be realized and address a relevant topic in the physics curriculum; thus, they appear appropriate to be used in high school and undergraduate physics courses.

‘Home made’ model to study the greenhouse effect and global warming

In this paper a simplified two-parameter model of the greenhouse effect on the Earth is developed, starting from the well known two-layer model. It allows both the analysis of the temperatures of the inner planets, by focusing on the role of the greenhouse effect, and a comparison between the temperatures the planets should have in the absence of greenhouse effect and their actual ones. It may also be used to predict the average temperature of the Earth surface in the future, depending on the variations of the concentration of greenhouse gases in the atmosphere due to human activities. This model can promote an elementary understanding of global warming since it allows a simple formalization of the energy balance for the Earth in the stationary condition, in the presence of greenhouse gases. For these reasons it can be introduced in courses for undergraduate physics students and for teacher preparation.

The surprising rolling spool: experiments and theory from mechanics to phase transitions

An asymmetric rolling spool can be investigated as a simple model for a second-order phase transition. At low energy it undergoes librational motion around the equilibrium position, whereas at high energies its motion becomes rototranslational. The analysis of its dynamics shows that when approaching critical energy, the period of oscillation diverges; and this suggests the transition from one phase to the other. We thus show that the concept of ‘phase transition’, useful to describe the behaviour of a variety of thermodynamic systems, can be actualized in this simple mechanical system. Moreover, a tight analogy can be found between the rolling spool’s behaviour and the Tomlinson model of sliding friction. This analogy makes it possible to interpret the critical switch of static friction near the threshold of motion as a phase transition. The rolling spool can be easily constructed and used as a hands-on experiment. Quantitative measurements of its motion were carried out through open-source video analysis software.

Studying motion along cycloidal paths by means of digital video analysis

The motion of a pendulum whose mass is constrained to move on a cycloid path and of a small sphere running on a frictionless cycloid track are investigated theoretically and experimentally. Measurements are carried out through analysing videos acquired using a digital camera by means of open-access video analysis software. The results obtained are in agreement with theoretical expectations. The topic, the accessibility of the experiments and the level of analysis are appropriate for an undergraduate classical mechanics course.