Search

The drag effect on a falling ball caused by air is a conventional subject in the most well-known textbooks of classical mechanics and fluid dynamics. Further, there are some papers that employ video analysis to track objects movements in the air making it possible to obtain position data as a function of time and its graphs. However, none of them addresses the case of a ball thrown downwards, maybe because this situation is neglected by textbooks or probably due to the experimental difficulty to perform this kind of launch manually. In this paper, both the fall and the vertical launch down of five different Styrofoam balls are filmed with an ordinary smartphone camera and analysed by using the free software Tracker. The position and velocities graphs depicted clearly the air drag effect on the ball's movements. The entire raw data are compared with a theoretical model and therefore terminal and initial velocities can be extracted as adjusted parameters from simple mathematical fits. The Reynolds number and the drag coefficient calculated for each ball agree with those found in the literature.

In general, undergraduate experimental physics laboratories do not usually have experiments designed to address rolling friction and to measure the value of the rolling friction coefficient. This work explores an experiment, which has the potential to arouse students' curiosity about rolling friction by addressing a counterintuitive aspect of the behavior of a sphere that rolls up, stops and then rolls down on an inclined track. In fact, due to the difference in the net static friction in the upward and downward movements caused by the rolling friction term, the sphere's acceleration when rolling upward is higher than when rolling downward. This difference, which had been predicted theoretically, was easily demonstrated graphically by video analysis, using both rubber and mouse balls. For two steel balls, this difference was more subtle, but it was still possible to detect it numerically. The experimental setup employed typical laboratory equipment and the free video analysis software "Tracker" to collect position and velocity data. The rolling friction coefficient was calculated with good precision by means of an angular coefficient of a fitted first-degree function involving appropriate variables.

Currently, the number of smartphones with an embedded gyroscope sensor has been increasing due games whose performance relies on 3D augmented reality. In general, teaching papers on the gyroscope sensor address very simple spatial configuration, where the fixed rotation axis coincides to the z-axis of the smartphone. This work presents five experimental setups with different spatial orientations of a smartphone on a turntable. The total angular velocity vector of the turntable is constant, but its projections on the three fixed Cartesian axes of the smartphone varies for the five spatial orientations investigated. For the sake of consistency, the magnitude of the vector sum of the three angular velocities components yielded by the gyroscope sensor was checked by video analysis using the free software, Tracker. The internal consistency between the results provided by this video analysis technique and data from the gyroscope assures us this sensor is reliable for teaching proposals. The main goals of this paper are (1) encourage teachers to effectively incorporate the gyroscope sensor of smartphones in to their classrooms, especially in high schools and undergraduate physics and engineering courses; (2) spread in the academic syllabus the Tait-Bryan convention, a very intuitive way to perform 3D rotations and; (3) explain how to interpret data of the three components of angular velocity obtained by the gyroscope sensor in different spatial orientations.

Nowadays, in almost any country in the world, it is difficult to find a young person who has never played with, seen, or heard of the most famous toy in 2017: the fidget spinner. According to Wikipedia: "The fidget spinner is a toy that consists of a ball-bearing in the center of a multi-lobed flat structure made from metal or plastic designed to spin along its axis with little effort." Articles on educational proposals related to fidget spinners have been presented recently. Naturally, an issue arises from this polemic context: can fidget spinners be used to illustrate or explain physics concepts such as moment of inertia, torque, and angular momentum? This paper presents a simpler, cheaper, and easier experimental setup to obtain moments of inertia of the fidget spinner by using the free software Tracker for video analysis. A consistency test with an aluminum cylindrical shell ensures the reliability of the experimental setup.

This work presents an experimental approach to Fermat's principle using a video analysis investigation applied to two high school classes whose students have basic knowledge of kinematics. The results indicate that without knowledge of advanced calculations, the students could verify the minimum time required for the light to travel between the two points compared to other alternative paths. This work aims to advise students to genuine scientific investigations, as contemporary literature demands. [ABSTRACT FROM AUTHOR]

This work presents a low-cost experiment to investigate heat conduction inside potato cubes, using thermistors as a thermometric instrument and Arduino as a data acquisition platform. In the theoretical framework, a heuristic argument was proposed to switch the 3D heat equation to an equivalent and simpler 1D equation, which is valid only along points on the cube's symmetry axis. In the experimental domain, an empirical and realistic time-dependent temperature function was used as boundary conditions instead of assuming simple boundary conditions, i.e., the temperature of the cube surface in contact with the air is kept constant. An approximate solution of the one-dimensional heat equation with nonhomogeneous and time-dependent empirical and actual boundary conditions was provided. Adjusting the experimental data to the theoretical solution predicted by the heat equation provides the thermal diffusivity of the potato. The thermal diffusivity obtained agrees with the reference values found in the literature. [ABSTRACT FROM AUTHOR]

Copyright of Caderno Brasileiro de Ensino de Física is the property of Caderno Brasileiro de Ensino de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Caderno Brasileiro de Ensino de Física is the property of Caderno Brasileiro de Ensino de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Caderno Brasileiro de Ensino de Física is the property of Caderno Brasileiro de Ensino de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work presents a proposal of a teaching activity that uses a simulation and a ludic experiment as a form of didactic transposition for the teaching of the apparent retrograde motion of Mars. This simulation was performed by a free software called Stellarium. In turn, the experiment used two fidget spinners coupled in order to make an analogy with the orbital movement of Earth and Mars. Both in the simulation and experiment it was made a video analysis using a free software called Tracker. The activity was ordered in the following steps: 1) Present the simulation and its video analysis to illustrate the relative movement of Mars considering the referential frame of the Earth; 2) Present the video analysis of the coupled fidget spinners movement in three different references frames, similar to the references frames of the Sun (heliocentric model), the Earth (geocentric model) and the Mars; 3) Present the video analysis of the center of mass of the fidget spinners and qualitatively describe the use of the heliocentric model, in the description of the movements of the planets of the solar system. [ABSTRACT FROM AUTHOR]

Could the world-famous fidget spinner toy be used in the classroom to illustrate the concepts of moment of inertia, torque and angular momentum? Curiously, there are very few papers related to the topic that have been published so far. In this work, we present a real situation consisting of two extremely simple experimental configurations of oblique launching of a spinner with and without initial spin type rotation. We define spin type rotation as any rotation in which the spinner rotates around one of its main symmetry axes. The technique chosen for data collection was the video analysis, using the free software Tracker. The main results were (i) To present a fast and easy execution experiment that simultaneously approaches the concepts of torque, orbital angular momentum and spin angular momentum. (ii) Analyze in a qualitative way the similarities and differences between the orientations of the orbital and spin angular momenta for two types of oblique launching (iii) Obtain a quantitative estimative of the magnitudes of the spin angular momenta in relation to the respective symmetry axis of the spinner, in both cases. [ABSTRACT FROM AUTHOR]

Copyright of Caderno Brasileiro de Ensino de Física is the property of Caderno Brasileiro de Ensino de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In general, the articles in the teaching area on pulses propagation or standing waves use very light wires or whose weights are negligible compared to the applied tensions. This approach both simplifies the wave equation making it linear as the relationship between the tension and the speed of the wave. However, this procedure restricts the experiments and requires the use of sensors and/or more expensive equipments to extract reliable data. In contrast, the aim of this work was to create and analyze a cheap and efficient educational experiment to obtain the relationship between the speed and the tension of a pulse and the linear density of a rope, whose mass was not negligible. In this situation, the rope is not straight, but hangs due to its own weight forming a curve called catenary. For data collection were employed only a camera of a smartphone and a free video analysis software. Different theoretical models applied in interpreting the results enabled a wide and deeper understanding of the experiment. The results showed a variation in the accuracy and precision according to the mathematical models adopted. This provided an interesting view, that is, the experimental work depends not only on the equipment used, but is entangled with the respective theories. Also, the different ways of modeling the same phenomenon, with a gradation of complexity, provide approaches adjusted to the high school and superior levels as well as for the various undergraduate courses. [ABSTRACT FROM AUTHOR]

The introductory textbooks on classical mechanics are extremely brief in addressing impulsive forces and the concept of impulse. This can be explained by the emphasis on the study of physical situations in which the applied forces are all constant or position dependent, but constant in time, which is the class of the so-called conservative forces. When the impulsive forces are referred to, they are generally illustrated by a quick blow on a ball, as in golf, tennis or baseball. The focus is still to turn the time dependent force into a constant average force, whose impulse is equivalent to the real force. This paper proposes a simple experiment that consists in applying with the fingers an impulsive force on a smartphone and record the time dependence of the force through its internal accelerometer. This technology allows obtaining the values of the speed during the applied impulsive force by iterating the data extracted of acceleration and time. Some interesting aspects neglected in books emerge from this analysis, such as the lack of symmetry of the applied impulsive force, the possibility of modeling the full interaction without appeal to the concept of average force and calculating impulse directly by impulse and linear momentum theorem. As a consequence of the experiment, it is also possible to obtain the kinetic friction coefficient between the smartphone and the horizontal surface. [ABSTRACT FROM AUTHOR]

Temperature measurements in undergraduate laboratories often do not take into account the dead time of the sensors and measurement systems, whether analogic or based on electronic data acquisition. This paper presents measurements and comparisons of different types of dead time thermometers, as well as some possibilities and strategies for adaptation and control of this limitation in experiments involving temperature measurements of liquids. [ABSTRACT FROM AUTHOR]

The dance of the pendula is the fascinating movement of a set of simple pendula arranged side by side. When they oscillate, sometimes present a synchronized movement, sometimes it seems to be disordered. However, this set of pendula can be prepared in many ways and each of them will culminate in different movements showing an experiment with multiple faces. In this work, the length of the pendula decrease linearly, being necessary to propose a theoretical model that describes this particular movement, based on the dependence of the lengths as a function of their positions. The study of the dance of the pendula is done by video analysis technique to visualize the movement frame by frame using the software Tracker, enabling to compare the proposed theoretical model with the obtained experimental data. [ABSTRACT FROM AUTHOR]

The teaching laboratories of experimental physics, both at high school and at undergraduate level, do not usually address didactic experiments that include the measurement of the rolling friction coefficient. Indeed, the concept of rolling friction is systematically ignored in the collections of high school and even those of university education. In this paper we propose a low cost experiment using just an ordinary cylindrical battery, a smartphone camera and the free software Tracker for video analysis. Moreover, integrated into one didactical experience, one can measure two distinct physical quantities, namely kinetic and rolling friction coefficients. In fact, the video-analysis of the complete cylindrical battery movement, launched manually on a flat horizontal surface, allows splitting the movement in two parts: rolling with slip followed by rolling without slipping. The Tracker software has proven to be an efficient tool for obtaining measurements of the center of mass position and time in both phases of the movement. The experimental results allow very accurate and precise calculations of various theoretical parameters, in particular the two friction coefficients. [ABSTRACT FROM AUTHOR]

Chlorine atoms released in the upper atmosphere from CFC and HCFC compounds when impacted by energetic particles are recognized as the main mechanism for the enlargement of the hole in the ozone layer. A recent study showed a strong indication that the chlorine atom could be released from CHClF₂ due to the ionization of either chlorine or fluorine present in the molecule. Investigation of the possible pathways for the dissociation of chlorine from CHClF₂ by electron impact has been performed by scanning its relative contribution to Cl production along the 2p fluorine threshold and by measuring the energy distributions of the fragments produced by this collision for energies below and above the 2p fluorine threshold using the new delayed extraction time-of-flight technique. The data presented here provide the kinetic energy distribution of the fragments emerging from the collision and show direct experimental evidence that the release of chlorine can be triggered by the removal either of a chlorine electron or of a non-bonding fluorine electron, a result that should also apply to photoionization. [ABSTRACT FROM AUTHOR]