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To perform a reliable video analysis, it is mandatory to avoid shaking the camera while taking the video, normally using a tripod for smartphones/cameras. But there are some situations which the only chance to make the video is using your hands and it is almost impossible to avoid shaking the camera even trying your best. Imagine the following situation: a volleyball is obliquely launched, and the video is filmed by hand. Then, a point that is fixed in relation to the ground is chosen as the origin of a ground fixed reference frame. Despite being a ground fixed point, it will appear shaky in images captured by the handheld camera. Thereby, two standard video analyses are performed, one from the ground fixed point random shaking and one from the ball’s trajectory, both in relation to the default reference frame of the video analysis software. Lastly, to implement the video analysis of the relative ball movement it is enough to subtract the position coordinates of the ball’s movement by the position coordinates of the ground fixed point tremble, at each instant of time. The graphs of the position and velocity components versus time are presented, and the results are discussed. Em uma videoanálise confiável, evita-se balançar a câmera durante a filmagem, normalmente usando um tripé para smartphones/câmeras. Mas existem algumas situações em que a única chance de fazer o vídeo é usando as mãos e é quase impossível evitar balançar a câmera mesmo tentando o seu melhor. Imagine a seguinte situação: uma bola de vôlei é lançada obliquamente e o vídeo é filmado à mão. Em seguida, um ponto que é fixo em relação ao solo é escolhido como a origem de um referencial fixo do solo. Apesar de ser um ponto fixo no solo, ele aparecerá trêmulo nas imagens capturadas pela câmera. Desse modo, duas videoanálises padrão são realizadas, uma do tremor aleatório do ponto fixo no solo e outra da trajetória da bola, ambas em relação ao referencial padrão do software de análise de vídeo. Por fim, para implementar a videoanálise do movimento relativo da bola, basta subtrair suas coordenadas de posição pelas coordenadas de posição do ponto fixo do solo, a cada instante de tempo. Esta técnica reduz drasticamente o efeito de vibração nas variáveis cinemáticas. Os gráficos dos componentes de posição e velocidade em função do tempo são apresentados e os resultados são discutidos.

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.

Resumo O momento angular de um sistema de partículas e a sua divisão em um termo orbital e um termo de spin é um assunto normalmente relegado a segundo plano, ou mesmo ausente, nas disciplinas introdutórias de mecânica dos cursos de graduação. Além disso, a conservação do momento angular de um sistema, na ausência de torques externos, pode ser muitas vezes contraintuitiva. O presente trabalho se utiliza de um brinquedo chamado flat ball, que têm um formato semelhante a discos, no contexto de uma colisão bidimensional. Duas flat balls idênticas são lançadas girando em sentidos opostos e colidem, sobre uma superfície de atrito desprezível. O experimento tem grande potencial pedagógico porque proporciona uma análise qualitativa e quantitativa das grandezas momentos linear e angular do sistema, bem com a sua conservação, empregando a técnica de videoanálise. O resultado surpreendente do experimento tem o potencial de despertar a curiosidade dos estudantes, bem como abre o caminho para abordar a transição dos módulos do momento angular orbital e de spin do sistema, antes e depois da colisão.

Resumo Este trabalho apresenta um recurso didático experimental em alternativa aos clássicos experimentos para verificação da lei de Hooke e daqueles que utilizam sensores eletrônicos para o estudo de forças atuantes em estruturas estáticas. Desenvolvemos uma maquete de uma estrutura típica em treliças triangulares simples para pontes, com molas acopladas em cada barra da estrutura. Com essa maquete, é possível explorar as potencialidades para a obtenção de resultados qualitativos e quantitativos sobre as forças que atuam nas barras da estrutura. As molas acopladas às barras da estrutura tem o propósito de nos permitir a visualização do comportamento de compressão ou tração e obter dados por medição direta das forças axiais atuantes em cada barra utilizando a lei de Hooke. Comparamos os valores experimentais das forças axiais de cada barra por medição direta com os resultados obtidos pelo método dos nós. Os resultados qualitativos e quantitativos dessa comparação indicam a viabilidade da utilização da maquete para fins didáticos. Abstract This work presents an experimental teaching resource as an alternative to the classic experiments to verify Hooke's law and those that use electronic sensors to study forces acting on static structures. We developed a model of a typical structure in simple triangular trusses for bridges, with springs attached to each member of the structure. With this model, it is possible to explore the potential for obtaining qualitative and quantitative results on the forces acting on the members of the structure. The springs coupled to the structure's bars have the purpose of allowing us to visualize the compression or traction behavior and obtain data by direct measurement of the axial forces acting on each member using Hooke's law. We compare the experimental values of the axial forces of each member by direct measurement with the results obtained by the method of joints. The qualitative and quantitative results of this comparison indicate the feasibility of using the model for educational purposes.

Resumo Este trabalho apresenta uma possibilidade de montar um interferômetro similar ao empregado no famoso experimento de Michelson e Morley utilizando materiais de fácil acesso e a um custo muito inferior que os experimentos didáticos disponíveis no mercado. Neste artigo, o principal desafio é o de mover um dos espelhos por poucos milímetros, o que é possível usando um sistema confeccionado para esse fim, similar a uma alavanca. O alinhamento é outro grande desafio da montagem aqui proposta. Aqui se apresenta um dispositivo alternativo que possibilita o alinhamento do feixe com precisão suficiente para medir o comprimento de onda da luz do laser com erro relativo de 4%. Abstract This work presents a possibility to carry out an interferometer, similar to the one used in the famous Michelson and Morley experiment, using easy access materials and at a much lower cost than the didactic experiments available in the market. The main challenge of this article is to move one of the mirrors by a few millimeters, which is possible using a home-made system similar to a lever. Alignment is another major challenge in this article. Here an alternative device is presented which enables the beam alignment with enough precision to measure the laser wavelength within 4% relative error.

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.

Momentum-resolved scattering experiments with laser-cooled atomic targets have been performed since almost two decades with MOTRIMS (Magneto-Optical Trap Recoil Ion Momentum Spectroscopy) setups. Compared to experiments with gas-jet targets, MOTRIMS features significantly lower target temperatures allowing for an excellent recoil ion momentum resolution. However, the coincident and momentum-resolved detection of electrons was long rendered impossible due to incompatible magnetic field requirements. Here we report on a novel experimental approach which is based on an all-optical $^6$Li atom trap that -- in contrast to magneto-optical traps -- does not require magnetic field gradients in the trapping region. Atom temperatures of about 2 mK and number densities up to 10$^9$ cm$^{-3}$ make this trap ideally suited for momentum-resolved electron-ion coincidence experiments. The overall configuration of the new trap is very similar to conventional magneto-optical traps. It mainly requires small modifications of laser beam geometries and polarization which makes it easily implementable in other existing MOTRIMS experiments., submitted to Phys. Rev. A

No presente trabalho discutimos a abordagem utilizada por alguns livros didáticos de física de nível médio sobre o fenômeno da refração luminosa. Nos capítulos introdutórios à refração da luz, imagens de objetos parcialmente imersos em recipientes preenchidos com água, apresentam-se “quebradas” e, em alguns casos, “separadas”, quando vistos lateralmente. Além de caracterizar os livros didáticos dentro de um conjunto de critérios estabelecidos, apresentamos também uma proposta experimental com o intuito de aprofundar a discussão acerca do tema. Usando a lei de Snell-Descartes, mostramos medidas relacionadas às posições das imagens formadas a partir de um canudo parcialmente imerso em diferentes níveis de água para dois tipos de recipientes: um de base circular e outro retangular. In the present work we discuss the approach used by some high school physics textbooks about the phenomenon of light refraction. In the introductory chapters to the refraction of light, images of objects partially immersed in containers filled with water are presented ”broken” and, in some cases, ”separated”, when viewed laterally. Besides characterizing the textbooks within a set of established criteria, we also present an experimental proposal with the intention of deepening the discussion about the theme. Using the Snell-Descartes law, we show measures related to the positions of images formed from a straw partially immersed in different water levels for two types of containers: one of circular base and another rectangular.

Neste trabalho propomos e investigamos uma proposta didática para o ensino de espelhos esféricos baseada na associação entre uma metodologia de aprendizagem ativa com a estratégia de analogias ponte e conceitos âncora. A atividade era constituída por dois experimentos sucessivos sobre as características de imagens virtuais conjugadas por um espelho esférico côncavo e a dependência de seu tamanho relativo com a posição do observador (ângulo visual). O público-alvo era composto por quatro turmas distintas de ensino médio de uma escola da rede federal. Todo o procedimento foi acompanhado de um material escrito na forma de questionário. Para analisar qualitativamente os diferentes tipos de resposta e também a evolução dos estudantes foi utilizada a taxonomia de reações de Chinn e Brewer. Os resultados obtidos revelam as seguintes conclusões: (i) Ratifica a crítica presente na literatura que o emprego isolado do conflito cognitivo não conduz a mudanças significativas nos conceitos prévios da grande maioria dos alunos. (ii) A estratégia de associar uma metodologia de aprendizagem ativa que provoque o conflito cognitivo com as analogias ponte foi bem sucedida em viabilizar uma mudança da teoria da maioria dos alunos (iii) A necessidade de pesquisas quantitativas complementares para avaliar ganhos de aprendizagem. In this paper we propose and investigate a teaching proposal about convergent mirror based on the association between an active learning methodology and method of bridge analogies and anchorings concepts. The activity consisted of two successive experiments on the characteristics of virtual images formed by the concave spherical mirror and dependence on their relative size with the observer position (visual angle) were. Four high school distinct classes of the federal system of education formed the target audience. The whole procedure was accompanied by a written material as worksheets. To evaluate qualitatively their different types of reaction and also the evolution facing the anomalous data from the first experiment, we used the reactions taxonomy created by Chinn and Brewer was used. The results show the following conclusions: (i) it ratifies the present criticism in the literature that the isolated use of cognitive conflict does not lead to significant changes in the previous conceptions of most pupils; (ii) The strategy of associating an discrepant experiment causing cognitive conflict with another bridge experiment, of predictable result that rescue anchoring correlated ideas by analogy, has been successful in achieving a theory change in the most of students; (iii) The need for further quantitative research to evaluate learning gains.

Neste trabalho são discutidos os resultados de uma sequência didática baseada no método Peer Instruction para o ensino de circuitos elétricos, aplicada em sete turmas de ensino médio integrado a cursos técnicos. Os dados obtidos, em dois testes iguais, antes e depois da aplicação do método, foram analisados a partir do ganho normalizado ou ganho de Hake, e comparados a trabalhos na literatura nacional e internacional. Os resultados revelam que seis delas apresentaram ganhos compatíveis com aqueles esperados para turmas submetidas a estratégias de aprendizagem ativa, de acordo com a literatura nacional. Por outro lado, somente os resultados apresentados por três turmas permitiriam classificá-las como turmas em que ocorreu aprendizagem ativa, considerando valores estabelecidos na literatura internacional. Nossos resultados corroboram a ideia de que a sequência didática pode ser utilizada como mediadora da relação ensino-aprendizagem para a discussão de circuitos elétricos.

Em geral, os artigos na área de ensino sobre propagação de pulsos ou de ondas estacionárias utilizam fios ou arames muito leves, cujos pesos são desprezíveis diante das tensões aplicadas. Essa aproximação simplifica tanto a equação de onda, tornando-a linear, como a relação entre a tensão e a velocidade da onda. Entretanto, esse procedimento restringe os experimentos e exige o uso de sensores e/ou equipamentos mais caros para extrair dados confiáveis. Diferentemente, o objetivo deste trabalho foi criar e analisar um experimento didático barato e eficiente para a obtenção da relação entre a velocidade e a tensão de um pulso e da densidade linear de uma corda, cuja massa não fosse desprezível. Nessa situação, a corda não fica em linha reta, mas pende devido ao seu próprio peso formando uma curva chamada catenária. Para a coleta de dados, foram empregados somente uma câmera de filmagem de um smartphone e um software gratuito de videoanálise. Os diferentes modelos teóricos aplicados na interpretação dos resultados permitiram uma compreensão mais ampla e profunda do experimento. A análise dos resultados revelou uma variação da acurácia e precisão de acordo com os modelos matemáticos adotados. Isso possibilitou uma interessante visualização de que o trabalho experimental não depende somente dos equipamentos empregados, mas é indissociavelmente entrelaçado com as respectivas teorias. Além disso, as diferentes formas de modelar um mesmo fenômeno, com uma gradação de complexidade, proporcionam abordagens ajustadas para os níveis médio e superior, bem como para os diversos cursos de graduação. 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.

Matrix Isolation Sublimation has generated cold atomic and molecular beams, detected via laser absorption spectroscopy. A time-of-flight spectrometer, based on low energy photoelectrons beams, allows identification of the various species formed in the neon matrix.

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 (i) encourage teachers to effectively incorporate the gyroscope sensor of smartphones in to their classrooms, especially in high schools and undergraduate physics and engineering courses; (ii) spread in the academic syllabus the Tait–Bryan convention, a very intuitive way to perform 3D rotations and; (iii) explain how to interpret data of the three components of angular velocity obtained by the gyroscope sensor in different spatial orientations.

In the present work, we develop a low-cost and simple experiment to visualise Fourier's synthesis using a short, soft, and light plastic coiled spring oscillating in a horizontal plane, and a basic camera (120 fps). It is shown that the spring obeys a linear wave differential equation, as gravitational influence is neglected. A nonlinear criterion is evaluated to determine if magnitudes of the parameters in the initial conditions satisfy the linear wave equation. Our setup promotes some desirable characteristics that make Fourier's synthesis experiments feasible, visual, and enlightening: (i) it requires few, common, and cheap resources, and the experiment can be carried out even in a high-school laboratory; (ii) since the spring's tension is small (~1 N, on average), the frequencies of normal modes are low (close to 2 Hz), and therefore, it is possible to record the oscillations just with the camera and extract a considerable number of position and time data in just one cycle; (iii) when the video is loaded in the Tracker free software, it can be reproduced in slow motion. Since the frequencies involved are low, an interesting and instructive temporal sequence of images of the spring displaying the typical trapezoidal shape appears clearly; (iv) the tools associated with the Tracker software tools can yield the relevant oscillation parameters, such as the damping constant, amplitudes, frequencies, and phases; and (v) it is possible to carry out superposition of a snapshot of the spring in Tracker at any time, and to draw the related Fourier synthesis graphs. The visual match between the shape of the spring and the theoretical graph is remarkable, and can be enhanced by adding the damping term.

Os roteiros e livros que servem de guias para o ensino de Mecânica nos laboratorios didaticos de fisica experimental no ensino superior costumam apresentar uma experiencia que consiste em abandonar uma esfera metalica do topo de uma plataforma de lancamento curva suspensa por um suporte apoiado sobre uma bancada. Ao alcancar a base da plataforma, a esfera e lancada horizontalmente deixando marcado o seu alcance em uma folha com o auxilio do papel carbono. Essa experiencia serve para ilustrar a conservacao da energia mecânica, supondo a hipotese de que a esfera execute um rolamento puro, bem como mostrar a importância de levar em conta a sua energia cinetica de rotacao. Contudo, na forma como o experimento e tradicionalmente apresentado nao ha uma descricao em tempo real do movimento e por isso nao e possivel perceber que a esfera desliza e rola na maior parte do percurso, so alcancando a condicao de rolamento puro ao final da plataforma. Esse equivoco no tratamento e o motivo da sistematica diferenca entre o balanco de energia previsto e aquele obtido pelas medidas experimentais. Neste trabalho, desenvolvemos um modelo teorico que considera tanto a curvatura da plataforma como os efeitos de borda devido ao encaixe parcial da esfera na largura da calha. Atraves da videoanalise extraimos dados experimentais do movimento completo que ilustram claramente uma transicao do rolamento com deslizamento para o rolamento puro para diferentes ângulos de inclinacao inicial analisados, bem como obtemos o valor aproximado do tempo de transicao para um dos casos.

A dança dos pêndulos é o fascinante movimento de um conjunto de pêndulos simples dispostos lado a lado que, ao serem postos a oscilar, ora apresentam um movimento sincronizado, ora aparentemente desordenado. Entretanto, esse conjunto de pêndulos pode ser elaborado de inúmeras formas e cada qual culminará em movimentos diferentes mostrando-se um experimento com múltiplas faces. Neste trabalho, os pêndulos que fazem parte do conjunto possuem comprimentos diferentes que decrescem linearmente, sendo necessário propor um modelo teórico que descreva este movimento em particular, baseado na dependência dos comprimentos dos pêndulos em função das suas posições. O estudo da dança dos pêndulos é feito pela técnica de vídeoanálise que permite visualizai¹ o movimento quadro a quadro utilizando o software livre Tracker, tornando possível confrontar o modelo teórico proposto com os dados experimentais obtidos.

We present high-resolution momentum distributions of ions and electrons created in single ionization of He, Ne and Ar targets by intense (0.15–2 PW cm−2) short-pulsed (25 fs) linearly polarized laser fields in the direction perpendicular to the polarization. Instead of a Gaussian shape predicted by standard tunnelling theory, the experimental data exhibit a sharp cusp-like peak at zero transverse momentum. The comparison of experimental data with (i) calculations performed within the strong-field approximation employing a Coulomb–Volkov wavefunction to model the final electron state and (ii) results of recent semiclassical calculations, shows that the 'cusp' appears due to the long-range Coulomb interaction between the emitted electron and the remaining ion. A similar structure was previously observed for ion–atom collisions.

We present the results of a systematic experimental study of dissociation and Coulomb explosion of molecular hydrogen induced by intense ultrashort (7–25 fs) laser pulses. Using coincident recoil-ion momentum spectroscopy we can distinguish the contributions from dissociation and double ionization even if they result in the same kinetic energies of the fragments. The dynamics of all fragmentation channels drastically depends on the pulse duration, and for 7 fs pulses becomes extremely sensitive to the pulse shape.

The ion momentum spectra for nonsequential double ionization of rare gases (He, Ne and Ar) in 23 fs 795 nm laser pulses were measured in the intensity range 0.075–1.25 PW cm−2. In the studies published, confusing differences in the shape of momentum distributions among different targets are consistently explained within a recollision scenario: excitation during recollision plus subsequent field ionization, not implemented in most theoretical approaches, evidently plays a decisive role for He and Ar nonsequential double ionization whereas it plays only a minor role for Ne.

Os laboratórios didáticos de física experimental, tanto no ensino médio quanto no ensino superior, não costumam abordar experimentos didáticos que contemplem a medida do coeficiente de atrito de rolamento. Aliás, o próprio conceito de atrito de rolamento é sistematicamente ignorado nas coleções de ensino médio e até mesmo naquelas de ensino superior. Neste artigo propomos um experimento de baixo custo usando apenas uma pilha média comum, uma câmera de smartphone e o software livre Tracker para vídeo-análise. Além disso, integramos em uma só experiência didática a medida de duas grandezas físicas distintas, a saber, o coeficiente de atrito cinético e o coeficiente de atrito de rolamento. De fato, a vídeo-análise do movimento completo da pilha, lançada manualmente sobre uma superfície horizontal plana, permite dividir o movimento em duas partes: rolamento com deslizamento seguido de rolamento sem deslizamento. O software Tracker provou ser uma ferramenta eficiente para a obtenção de medidas de posição do centro de massa e de tempo, nas duas fases do movimento. Com esses resultados foram calculados diversos parâmetros da teoria, em especial os dois coeficientes de atrito, com bastante acurácia e precisão. 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.

The spin-echo NMR technique was used to study the magnetic properties of the following intermetallic compounds of the Gd–Ni series: Gd 2 Ni 17 , GdNi 5 , GdNi 3 , GdNi 2 and GdNi, with 155 Gd and 157 Gd nuclei as local probes. These compounds have different crystal structures and order ferri- or ferromagnetically. The NMR measurements were performed at 4.2 and 1.5 K. The NMR spectra were compared to computed line positions obtained from the diagonalization of the complete hyperfine Hamiltonian. The RKKY contribution to the hyperfine field was computed for Gd 2 Ni 17 and GdNi 3 , and differences in the values of B hf at the two sites of Gd, of the order, respectively, of 18 and 6 T, were thus justified. An intense quadrupole interaction was observed at the Gd sites in the compounds GdNi 5 , Gd 2 Ni 17 , and in one of the sites of the compound GdNi 3 ; in all these cases, the values of V zz are of the order of 10 22 V/m 2 . The NMR results in GdNi are consistent with a direction of magnetization along the b -axis for this compound. The present study presents the first systematics of hyperfine interactions in Gd–Ni compounds.

A charge that moves along a closed path is normally ascribed a magnetic dipole moment. The interaction of such a circuit with an external magnetic field is usually described in terms of the interaction of the field with the magnetic moment. Whereas this might be the appropriate approach in most cases, it is not obvious that this should always be so. In this paper we calculate the trajectory and angular momentum of a particle with charge q and mass m, constrained to move on a spherical surface of radius a, in a static magnetic field B0, and compare it with the motion of a pointlike magnetic dipole in the same field. The regime of motion is governed by the ratio between two parameters: kL/, where L = -qB0/2m is the Larmor frequency, and = v0/a, where v0 is the initial velocity of the particle, is the angular frequency of the particle in the loop. For an arbitrary value of k the relation between the spherical coordinate of the particle, , and the time is given by the elliptical integral t = (1-k2cos2)-1/2 d, which reduces to the usual relation, = 2, where is the frequency, only for k<

The classical motion of a charged particle in oscillating magnetic and electric fields is investigated. Introducing a rotating coordinate system frame greatly simplifies the equations of motion and allows a formal analogy with the problem of three coupled oscillators with anisotropic damping. The solutions are calculated analytically. It is shown that when the resonance condition is achieved, that is, the frequency of the oscillating field equals the cyclotron frequency of the particle , the particle is confined to a region of space of volume given approximately by , where is the modulus of the initial velocity of the particle. is the frequency of the particle about , the magnitude of the oscillating field. The orbit of the particle is shown to be a closed curve in the rotating frame, or a closed surface in the laboratory system. Off resonance, the particle drifts away. We simulate the motion of particles with charge-to-mass ratios differing by about 1%, and show that they can be resonantly separated. The results suggest a resonant method for charged particle confinement and isotope separation.

We present initial-state selective fully differential cross sections for ionization of lithium by 24 MeV ${\mathrm{O}}^{8+}$ impact. The data for ionization from the $2s$ and $2p$ states look qualitatively different from each other and from $1s$ ionization of He. For ionization from the $2p$ state, to which in our study the ${m}_{L}=\ensuremath{-}1$ substate predominantly contributes, we observe orientational dichroism and for $2s$ ionization pronounced interference which we trace back to the nodal structure of the initial-state wave function.

Os livros didáticos de física utilizam a definição do aumento linear transversal (AL) com o objetivo de comparar o tamanho da imagem ao do objeto quando abordam espelhos e lentes esféricas. Este trabalho discute as distorções geradas pela utilização do conceito de AL e emprega o conceito de aumento angular (AA) para demonstrar que a visão do observador acerca do tamanho relativo entre o objeto e a sua imagem associada produzida por um espelho esférico côncavo depende da sua própria posição. Foi realizada uma análise qualitativa de dois experimentos, e ainda análises quantitativas e gráficas da variação do módulo do AA em função da posição do observador para os quatro tipos de imagens produzidas por um espelho côncavo. Discute-se a necessidade da introdução do conceito de aumento angular nos livros didáticos para compreender a visualização das imagens formadas por um espelho esférico côncavo. The physics textbooks use the definition of linear magnification (LM) in order to compare the size of the image with the object when addressing spherical mirrors and lenses. This work discusses the distortions generated by using the concept of LM and employs the angular magnification (AM) to show that the vision of the observer about to the relative size between the object and its associated image produced by concave spherical mirror depends on its own position. It was performed a qualitative analysis of two experiments, and even quantitative and graphics analysis of the modulus variation of AA as a function of the observer position for four types of images produced by a concave mirror. It is discussed the need of the introduction of the angular magnification concept in textbooks to understand the visualization of images formed by a concave spherical mirror.

In this work, the inclusion of an Einzel-like lens inside the time-of-flight drift tube of a standard mass spectrometer coupled to a gas cell-to study ionization of atoms and molecules by electron impact-is described. Both this lens and a conical collimator are responsible for further focalization of the ions and charged molecular fragments inside the spectrometer, allowing a much better resolution at the time-of-flight spectra, leading to a separation of a single mass-to-charge unit up to 100 a.m.u. The procedure to obtain the overall absolute efficiency of the spectrometer and micro-channel plate detector is also discussed.

In the predominant approach in physics textbooks, the collision between particles is treated as a black box, where no physical quantity can be measured. This approach becomes even more evident in experimental classes where collisions are the simplest and most common way of applying the theorem of conservation of linear momentum in the asymptotic behavior. In this paper we develop and analyse an experiment on collisions using only two smartphones. The experimental setup is amazingly simple; the two devices are aligned on a horizontal table of lacquered wood, in order to slide more easily. At the edge of one of them a piece of common sponge is glued using double-sided tape. By using a free smartphone application, the values generated by the accelerometer of the two devices in full motion are measured and tabulated. Through numerical iteration, the speed graphs of the smartphones before, during, and after the collision are obtained. The main conclusions were: (i) the demonstration of the feasibility of using smartphones as an alternative to air tracks and electronic sensors employed in a teaching lab, (ii) the possibility of investigating the collision itself, its characteristics and effects; this is the great advantage of the use of smartphones over traditional experiments, (iii) the compatibility of the results with the impulse-momentum theorem, within the margin of uncertainty.

A general method to measure the energy distribution function of molecular fragments using a pulsed electron beam with time-delayed extraction coupled to a time-of-flight spectrometer is presented. The energy distributions of the homoisotopic species ${}^{14,15}$N${}^{+}$ and ${}^{14,15}$N${{}_{2}}^{2+}$, with the same mass-to-charge ratio, produced by 35--400 eV electron impact ionization of N${}_{2}$, are disentangled, showing two independent fragmentation routes for N${}^{+}$ ions with kinetic energies smaller than 1.0 eV. No measurable isotopic effect was found, indicating that predissociation does not play a role in this region of impact energies.

We present a novel experimental tool allowing for kinematically complete studies of break-up processes of laser-cooled atoms. This apparatus, the 'MOTReMi,' is a combination of a magneto-optical trap (MOT) and a reaction microscope (ReMi). Operated in an ion-storage ring, the new setup enables us to study the dynamics in swift ion-atom collisions on an unprecedented level of precision and detail. In the inaugural experiment on collisions with $1.5\text{ }\text{ }\mathrm{MeV}/\mathrm{amu}$ ${\mathrm{O}}^{8+}$-Li the pure ionization of the valence electron as well as the ionization-excitation of the lithium target was investigated.

Utilizando garrafas PET é possível investigar a hidrodinâmica de fluidos incompressíveis. Comparações utilizando os resultados experimentais da cinemática podem ser feitas. Esta proposta didática de baixo custo é aplicada na parte experimental da disciplina Fluidos e Termodinâmica do curso de Licenciatura em Física do IFRJ - Campus Nilópolis. It is possible to investigate the hydrodynamics for incompressible fluids using PET bottles. Comparisons with experimental results of the kinematics can be done. This didactic proposal of low cost is applied at the experimental lectures of Fluids and Thermodynamics of the IFRJ Undergraduate Physics Course - Campus Nilópolis.

Fully differential data on H2(D2)-dissociation in carrier-envelope-phase (CEP)stabilized 6fs laser pulses were recorded with a reaction microscope. By varying the CEP control over the proton emission direction, and, thus, the charge localization was achieved.

Momentum distributions of ${\mathrm{Ne}}^{2+}$ and ${\mathrm{Ar}}^{2+}$ ions created by linearly polarized $795\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, $25\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ laser pulses have been traced at intensities from ${10}^{14}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}3\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ using a ``reaction microscope.'' Apart from the transition from nonsequential to sequential ionization, characterized by significant changes in longitudinal momentum distributions developing from a double hump, over a triple-peak structure to a narrow single Gaussian observed for both ions, for ${\mathrm{Ar}}^{2+}$ we find a similar behavior but reversed in its intensity dependence in the purely nonsequential regime, pointing to contributions of recollision excitation plus subsequent field ionization, or to the role of ``Z trajectories'' recently predicted within classical calculations.

We report on a kinematically complete experiment on nonsequential double ionization of He by 25 fs 800 nm laser pulses at 1.5 PW/cm{sup 2}. The suppression of the recollision-induced excitation at this high intensity allows us to address in a clean way direct (e,2e) ionization by the recolliding electron. In contrast with earlier experimental results, but in agreement with various theoretical predictions, the two-electron momentum distributions along the laser polarization axis exhibit a pronounced V-shaped structure, which can be explained by the role of Coulomb repulsion and typical (e,2e) kinematics.

O mergulhador cartesiano, ou ludião, é um aparato simples freqüentemente apresentado em feiras de ciências. É utilizado para ilustrar os princípios hidrostáticos de Pascal e de Arquimedes. Todavia, a simplicidade do aparato induz uma sobre-simplificação da descrição do experimento. Mesmo alguns livros didáticos fornecem explicações incompletas. Outro engano comum é a associação do mergulhador cartesiano com submarinos. O ludião é muito semelhante a outro tipo de equipamento subaquático, muito mais antigo que os submarinos, os sinos de mergulho. Neste trabalho, os aspectos práticos e a descrição teórica do experimento são abordados em detalhes. The Cartesian diver is a simple apparatus which is presented often in science fairs. It is used to illustrate the hydrostatic principles of Archimedes and Pascal. However the apparatus simplicity leads in general to an oversimplification description of the experiment. Even some textbooks give incomplete explanations. Another common misconception is to associate Cartesian divers with submarines. The Cartesian diver is very similar to another kind of subaquatic equipment older then the submarines the diving bells. In this work, the practical aspects and the theoretical description of the experiment are treated in details.

Target electron removal in Li2+-Li collisions at 2290 keV/amu is studied experimentally and theoretically for ground and excited lithium target configurations. It is shown that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. According to our calculations, the process is shown to be strongly single-particle like. On one hand, a high resemblance between theoretical single-particle ionization and exclusive inner-shell ionization is demonstrated, and contributions from multi-electron processes are found to be weak. On the other hand, it is indicated by the discrepancy between experimental and single-particle theoretical results that multi-electron processes involving ionization from the outer-shell may play a crucial role.

The spin echo 155 Gd and 157 Gd NMR was used to study the intermetallic compounds Gd 2 Ni 17 , GdNi 5 , GdNi 3 , GdNi 2 and GdNi. These compounds have different crystal structures and order ferri- or ferromagnetically. The measurements were performed at 4.2 and 1.5 K. The NMR spectra were compared to computed line positions obtained from the diagonalization of the complete hyperfine Hamiltonian. The differences in the values of B hf at the two sites of Gd in Gd 2 Ni 17 and GdNi 3 , of the order of 18 and 6 T, respectively, may be justified, in a semi-quantitative way, through the RKKY model. We observed a strong quadrupole interaction at the Gd sites in the compounds GdNi 5 , Gd 2 Ni 17 , and in one of the sites of the compound GdNi 3 ; in all these cases, the values of V zz are higher than 7.0 × 10 21 V/m 2 . The NMR results in GdNi are consistent with a direction of magnetization along the b -axis. No NMR signal could be unambiguously attributed to 61 Ni nuclei. This work presents the first NMR results of the Gd-Ni intermetallic compounds.

We present results of high resolution fully differential measurements on single ionization of He, Ne, and Ar by 7-25 fs linearly polarized 800nm laser pulses at intensities of up to 2.1015 W/cm2. Using a 'Reaction-Microscope' we were able to trace signatures of multiphoton ionization deep into the tunnelling regime. Surprisingly, in the low-energy electron spectra we observed several features (absence of the ponderomotive shifts, splitting of the peaks, their degeneration for few-cycle laser pulses) typical for resonantly-enhanced ionization. Other remarkable features, as the sharp cusp-like momentum distributions in the direction perpendicular to the laser field or the observed minima at zero longitudinal momentum for He and Ne, can be reproduced by semiclassical models, where the electron motion in the combined laser and Coulomb field is treated classically after the tunnelling.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present results of high-resolution experiments on single ionization of He, Ne and Ar by ultra-short (25 fs, 6 fs) 795 nm laser pulses at intensities 0.15-2.0x10^15 W/cm^2. We show that the ATI-like pattern can survive deep in the tunneling regime and that the atomic structure plays an important role in the formation of the low-energy photoelectron spectra even at high intensities. The absence of ponderomotive shifts, the splitting of the peaks and their degeneration for few-cycle pulses indicate that the observed structures originate from a resonant process., 11 pages, 3 figures

We present the results of the detailed experimental study of multiple ionization of Ne and Ar by 25 and 7 fs laser pulses. Whereas in multiple ionization of Ar different mechanisms, involving field ionization steps and recollision-induced excitations, play a role, for Ne only one channel, where the highly correlated instantaneous emission of up to four electrons is triggered by a recollisional electron impact, is found to be important. Using few-cycle pulses we are able to suppress those processes that occur on time scales longer than one laser cycle.

A new ultrahigh vacuum‐compatible (∼ 10−11 mbar) “reaction microscope” was built to investigate multiple ionization of atoms and molecules in ultra‐short (23 fs), intense laser pulses (1014 – 1016 W/cm2, 795 nm) . In first experiments ion momentum distributions for single and double ionization of noble gas atoms in the nonsequential and sequential intensity regime were measured using linearly polarized laser pulses. The apparatus is currently improved to perform measurements under even lower residual gas pressures (< 10−13 mbar). Furthermore, the new apparatus is ideally suited for future studies on dissociation and Coulomb explosion of molecules.