This work presents a new filming technique for objects captured in motion that minimizes the typical trail (blur) left in the recorded videos, increasing the accuracy of the video analyses. In order to reduce this trailing, we present a new technique called video analysis by stroboscopic illumination. The technique consists of filming the object of study illuminated only by short and intense pulses of light, without natural or artificial ambient lighting. An electronic device generates the pulses at a frequency adjustable to the frequency of the frames per second that take part in the video. As a result, we present an example of the proposed technique by filming a rubberized sphere launched from a ramp. This technique makes it possible to film by cell phones with low-resolution cameras and a low acquisition rate, allowing the improvement of the results of motion measurements. blur (blur videos analyses trailing illumination light lighting result ramp lowresolution resolution rate measurements

We present the video analysis of the oblique launch of five Styrofoam balls into the air, highlighting the effect of the drag force. Graphs of the trajectories, position, and velocity coordinates as a function of time are obtained numerically using the fourth-order Runge-Kutta method (RK4) and superimposed on the experimental data and compared to the ideal case without drag force. The values of the drag coefficients used in the RK4 numerical calculation are compatible with those presented in the literature. Measurements of each system’s kinetic, gravitational potential and mechanical energies, as well the modulus of the work of the drag force were obtained as a function of time, showing that the reduction in mechanical energy is more pronounced in the intervals where the variation of the kinetic energy is greater. air trajectories position fourthorder fourth order RungeKutta Runge Kutta RK (RK4 literature systems system s energies greater (RK

Apresentamos a videoanálise do lançamento oblíquo de cinco bolas de isopor no ar, evidenciando o efeito da força de arrasto. Gráficos das trajetórias, das coordenadas de posição e velocidade em função do tempo são obtidas numericamente pelo método Runge-Kutta de quarta ordem (RK4) e superpostas aos dados experimentais, sendo também comparadas ao caso ideal sem força de arrasto. Os valores dos coeficientes de arrasto utilizados no cálculo numérico RK4 são compatíveis com aqueles apresentados na literatura. Foram obtidas as medidas das energias cinética, potencial gravitacional, mecânica e do módulo do trabalho da força de arrasto de cada sistema em função do tempo, mostrando que a redução da energia mecânica é mais pronunciada nos intervalos onde a variação da energia cinética é maior. ar trajetórias RungeKutta Runge Kutta RK (RK4 experimentais literatura gravitacional maior (RK

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.

Abstract The angular momentum of a particle system and its division into an orbital term and a spin term is a subject usually relegated to the background, or even absent, in introductory mechanics courses in undergraduate courses. In addition, the angular momentum conservation of a system, in the absence of external torques, can often be counterintuitive. The present work uses a toy called flat ball, which has a format similar to discs, in the context of a two-dimensional collision. Two identical flat balls are launched spinning in opposite directions and collide on a negligible friction surface. The experiment has great pedagogical potential because it provides a qualitative and quantitative analysis of the magnitude of the linear and angular momenta of the system, as well as its conservation, using the technique of video analysis. The surprising result of the experiment has the potential to arouse students' curiosity, as well as opening the way to address the transition of the system's absolute values of the orbital angular momentum and spin angular momentum, before and after the collision.