Paulo Simeão Carvalho

Rotation in secondary school: teaching the effects of frictional force

Frictional force is a source of misconceptions among students, as teachers know from daily experience. This is confirmed by many studies carried out by investigators from all over the world. Surprisingly (or perhaps not), we have found some of these misconceptions among physics school teachers and senior students of physics education courses participating in a workshop in Portugal. In this article we discuss conceptual problems involving frictional force in rotating bodies and suggest teaching strategies based on problem solving, in order to ensure meaningful learning of this difficult topic.

Pyroelectric effect and freezing out of domain structure in betaine arsenate

Abstract This work reports some results concerning the study of pyroelectric effect in Betaine Arsenate ((CH3)3 NCH2 COO.H3 As O4). The pyroelectric coefficient along the crystallographic c-axis reveals two anomalies localized in the temperature range of 110–120 K. The existence of these two anomalies is confirmed by an experimental study of dielectric constant and dielectric loss in the same samples. We interpret the upper anomaly as that between a paraelectric and a mixed phase, i.e. a ferroelectric and structural glass and the lower one as a freezing temperature where the domain wall mobility is frozen out.

How to Determine the Centre of Mass of Bodies from Image Modelling.

Image modelling is a recent technique in physics education that includes digital tools for image treatment and analysis, such as digital stroboscopic photography (DSP) and video analysis software. It is commonly used to analyse the motion of objects. In this work we show how to determine the position of the centre of mass (CM) of objects with either isotropic or anisotropic mass density, by video analyses as a video based experimental activity (VBEA). Strobe imaging is also presented in an educational view, helping students to visualize the complex motion of a rigid body with heterogeneous structure. As an example, we present a hammer tossed with translation and rotation. The technique shown here is valid for almost any kind of objects and it is very useful to work with the concept of CM.

An Inexpensive Technique to Measure Coefficients of Friction with Rolling Solids

Frictional forces are everywhere. They are probably among the most important macroscopic forces in our daily routine because we depend on them to walk, to pick up objects, and even to eat! They affect our lives in different ways, and thus it is very important to understand them better; this is what we say to our students. There are many experimental methods and techniques to measure static and kinetic frictional forces (and to determine their corresponding coefficients of friction), which we can find in several textbooks.1–5 Most of them involve pulling/pushing blocks along a flat surface and expensive equipment for accurate measuring (sensors, computers, etc.). In this paper we show how to find both coefficients of friction, static and kinetic, with rolling objects instead of blocks in a very simple way and using nonexpensive laboratory equipment.

Using Image Modelling to Teach Newton's Laws with the Ollie Trick.

Image modelling is a video-based teaching tool that is a combination of strobe images and video analysis. This tool can enable a qualitative and a quantitative approach to the teaching of physics, in a much more engaging and appealling way than the traditional expositive practice. In a specific scenario shown in this paper, the Ollie trick, we show how image modelling can contribute to the contextualisation of Newtons Laws, foster an effective learning and spell out the relation between forces and the different moments of skateboarding.

A QUEDA DOS CORPOS PARA ALÉM DO QUE SE VÊ: CONTRIBUIÇÕES DAS IMAGENS ESTROBOSCÓPICAS E DA VIDEOANÁLISE PARA A ALFABETIZAÇÃO CIENTÍFICA

The importance of practical-experimental activities for a learning process in which the student can appropriate conceptual, epistemological and social elements of scientific knowledge has long been discussed. Thus, teachers use videos for systematic phenomenological observation in their classes, among other pedagogical tools. In this sense, stroboscopic images and video analysis are didactic resources produced from videos of moving bodies and, therefore, they broaden the spectrum of movements that can be proposed and studied in the classroom. In this context, we present in this thesis the results of a research that verified if these resources have potential for scientific education. The research presented here begins with a historical review of the invention of chronophotography and its applications in the context of Art, Science and Science Teaching, when they began to be called stroboscopic images; and continues, in the form of articles, with examples of possible learning contexts with video analysis and stroboscopic images With the purpose of verifying how the use of these didactic resources collaborate for the Scientific Literacy, we elaborated a didactic intervention, with methodology of Inquiry-based teaching, whose theme was the fall of the bodies. During the intervention, the discursive interactions among the students were recorded for later listening and transcription, in order to identify the Scientific Literacy Indicators and the presence of Toulmins Argumentative Patterns. The results showed that there was argumentation by the students and, from the Indicators of Scientific Literacy, it was revealed how the students constructed the same arguments. The results obtained with the research subjects were satisfactory for the use of the resources and the methodology of Inquiry-base teaching to promote Scientific Literacy.

Standing Waves in an Elastic Spring: A Systematic Study by Video Analysis.

The word “wave” is part of the daily language of every student. However, the physical understanding of the concept demands a high level of abstract thought. In physics, waves are oscillating variations of a physical quantity that involve the transfer of energy from one point to another, without displacement of matter. A wave can be formed by an elastic deformation, a variation of pressure, changes in the intensity of electric or magnetic fields, a propagation of a temperature variation, or other disturbances. Moreover, a wave can be categorized as pulsed or periodic. Most importantly, conditions can be set such that waves interfere with one another, resulting in standing waves. These have many applications in technology, although they are not always readily identified and/or understood by all students. In this work, we use a simple setup including a low-cost constant spring, such as a Slinky, and the free software Tracker for video analysis. We show they can be very useful for the teaching of mechanical w...

The centre of mass of a ‘flying’ body revealed by a computational model

The interpretation of complex trajectories of rigid bodies by the identification of their centre of mass (CM), has a large potential for improving the understanding of the concept of CM at college and university level. Therefore, it is not surprising that there are several techniques described in the literature concerning how to identify the CM of rigid bodies. However, these techniques fail when the CMs position in the bodys frame of reference changes when the body is at motion. In this work we present a computational model that allows the identification of the CM with very good accuracy, either when the CMs position changes or is fixed in the bodys frame of reference. This model can be used for a system of bodies moving in a plane, for which the CM of each body coincides with its geometric centre. The effectiveness of this model is tested with experiments using video acquisition and numerical analysis, and can be done in experimental classes under controlled conditions. Students are then able to compare the computed CM with the experimental CM, and investigate why the bodies sometimes present weird trajectories. This property applies in particular to sports, so the model can be also very useful as an educational resource for the explanation of the motion of athletes, namely as a tool for optimizing their performance.

How to study the Doppler effect with Audacity software

The Doppler effect is one of the recurring themes in college and high school classes. In order to contextualize the topic and engage the students in their own learning process, we propose a simple and easily accessible activity, i.e. the analysis of the videos available on the internet by the students. The sound of the engine of the vehicle passing by the camera is recorded on the video; it is then analyzed with the free software Audacity by measuring the frequency of the sound during approach and recede of the vehicle from the observer. The speed of the vehicle is determined due to the application of Doppler effect equations for acoustic waves.

Indução eletromagnética em laboratório

We studied the induction of an electromotive force caused by the magnetic field of a solenoid at various coils placed inside it. We used an experimental setup - provided by the learning laboratory infrastructure of the Physics Department at FCUP - to determine the dependence of the induced electromotive force with very different experimental variables, namely: number of coil turns, coil cross-sectional area, coil axis angle, angular frequency of the signal, and signal amplitude of current. The value of the vacuum permeability was determined, using this same method, and compared with the known value. This study aimed to develop a new pedagogical approach of the laws of electromagnetic induction. It also made a reflection on how to approach this experience in secondary education and what are the best techniques to perform, explore and evaluate the activity.