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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]

Objectives: To investigate the biochemical and morphological effects of ethanol (EtOH) binge drinking during pregnancy on parotid glands (PG), submandibular glands (SMG), and saliva of offspring rats. Methods: Pregnant Wistar rats (n = 8) were exposed to EtOH consumption (3 g/kg/day – 20 % w/v) for three consecutive days. The saliva of 40-day-old offspring rats was collected to determine amylase activity and total protein concentration. PG and SMG were collected to performe oxidative biochemistry, morphometric and immunohistochemistry analyses (Student’s t-test, p < .05). Results: EtOH consumption during pregnancy significantly decreased the total protein concentration and decreased amylase activity. In the PG, the EtOH group showed increased lipid peroxidation and decreased antioxidant capacity against peroxyl. In the SMG, the EtOH group showed increased lipid peroxidation and NOx metabolite levels. PG exposed to EtOH showed a decrease of acini, ducts, and total parenchymal area. SMG exposed to EtOH showed an increase in the total stromal area. The expression of CK-19 and Vimentin were found not different between groups. Conclusions: For the first time, a three-day EtOH binge-drinking protocol during pregnancy is associated with oxidative stress and morphometric alterations in the salivary glands of offspring rats and with the functional reduction of the main salivary enzyme (amylase). Clinical relevance: EtOH consumption during pregnancy altered the morphology and physiology of the salivary glands of offspring rats.

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]

Este trabalho analisa dados de 11 anos (1978-1988) de observações da fenologia de 2 espécies arbó­reas da família Lecythidaceae: Corythophora rimosa W. Rodrigues e Corythophora alta R. Knuth, incluindo as fases de floração, frutificação e mudança foliar.Determi­ nou-se a época, duração e freqüência das fases reprodutivas, bem como o tipo de mudança foliar. As espécies apresentaram a fase de floração nas estações de seca e de chuvas, porém, com maior ocorrência na época chuvosa, com assincronismo entre os individuas observado para C. rimosa. A fase de frutificação foi bservada principalmente na época de seca, com sincronismo entre os indivíduos. A duração média da fase de floração e frutificação para C. alta foi de 6 meses, e para C. rimosa 3 e 4 meses, respectivamente. A nível de espécie, o padrão de ocorrência da fase de floração e frutificação foi anual, porém a nível de indivíduo C. rimosa apresentou comportamento supra-anual. Quanto ao tipo de mudança foliar, as espécies apresentaram características de sempreverdes, com maior época de troca de folhas na estação seca. C. alta seria a únicaespécie que poderia cumprir um programa de coleta de sementes regular, para pesquisas tecnológicas e silvi­culturais. C. rimosa necessita de maiores informações para explicar sua biologia reprodutiva.

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]

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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]