IDENTIFICAÇÃO DAS CARACTERÍSTICAS ONDULATÓRIAS A PARTIR DO EXPERIMENTO DO PÊNDULO TRAÇADOR / IDENTIFICATION OF WAVING CHARACTERISTICS FROM THE TRACTION PENDULUM EXPERIMENT

Neste artigo apresentamos uma atividade experimental que é desenvolvida habitualmente no laboratório didático de Física do Colégio Militar de Porto Alegre. Com este experimento discutimos as características e propriedades de uma onda, formada a partir do que denominamos pêndulo traçador. O experimento consiste em um pêndulo simples, que é formado por um funil cheio de areia preso por um fio. Ao oscilar, o pêndulo deixa areia cair sobre um papel pardo no qual estão desenhados eixos horizontais e verticais representando um plano cartesiano. Após concluídas as oscilações, o desenho formado no papel pardorepresenta aquilo que denominamos uma onda. Nosso objetivo é apresentar o experimento para que outros professores possam incorporá-lo em sua prática escolar como forma de introduzir as características de uma onda. Verificamos, mediante aplicação de testes regulares, que a atividade experimental proposta foi importante para solucionar alguns problemas da prática escolar.

Finite Element Analysis and Experiment of the Bruise Behavior of Carrot under Impact Loading

Root–stem separating is one of the most important processes in carrot harvesting, but it is easy to cause damage due to the impact. In order to reduce the damage of carrot harvesting and provide the basis for the design of the separation mechanism, the damage mechanism of carrot was studied by the finite element method (FEM) and pendulum experiment in this study. Through the simulation analysis and the pendulum experiment, it was found that the critical damage impact force was 45.2 N and 43.1 N, respectively. Comparing the two results, the critical impact force of the carrot was basically the same, with an error of 4.87%. In conclusion, the FEM was reliable for the carrot damage prediction, and the critical impact force could be used for the design of a carrot harvesting mechanism.

Experiments in the Principia

Newton carried out four groundbreaking experiments in conjunction with the Principia and proposed a fifth. This chapter reviews his reasons for doing them, their design, and what they achieved. The four include a two-pendulum experiment early in 1685 to establish that the action of gravitational forces on a body is always proportional to its mass and hence that all bodies at any point respond to a gravitational force in the same way. In that same year he conducted a ballistic pendulum experiment to establish that this third law of motion holds for impact of spheres of a wide range of elastic responses, in the process identifying what became known as the coefficient of restitution. He carried out two sets of experiments measuring fluid resistance forces on spheres, the less than successful first relying on pendulum decay and then, for the second edition, vertical-fall. All five experiments were designed to “put the question to nature” in the sense that the three laws of motion enable their results to yield theory-mediated answers to theretofore open questions about forces—and thus parallel the answers to questions about celestial forces drawn from planetary motions that form the core of the Principia.

Design of a Flexure Based Low Frequency Foucault Pendulum

The Foucault pendulum is a well-known mechanism used to demonstrate the rotation of the Earth. It consists in a pendulum launched on linear orbits and, following Mach’s Principle, this line of oscillation will remain fixed with respect to absolute space but appear to slowly precess for a terrestrial observer due to the turning of the Earth. The theoretical proof of this phenomenon uses the fact that, to first approximation, the Foucault pendulum is a harmonic isotropic two degree of freedom (2-DOF) oscillator. Our interest in this mechanism follows from our research on flexure-based implementations of 2-DOF oscillators for their application as time bases for mechanical timekeeping. The concept of the Foucault pendulum therefore applies directly to 2-DOF flexure based harmonic oscillators. In the Foucault pendulum experiment, the rotation of the Earth is not the only source of precession. The unavoidable defects in the isotropy of the pendulum along with its well-known intrinsic isochronism defect induce additional precession which can easily mask the precession due to Earth rotation. These effects become more prominent as the frequency increases, that is, when the length of the pendulum decreases. For this reason, short Foucault pendulums are difficult to implement, museum Foucault pendulum are typically at least 7 meters long. These effects are also present in our flexure based oscillators and reducing these parasitic effects, requires decreasing their frequency. This paper discusses the design and dimensioning of a new flexure based 2-DOF oscillator which can reach low frequencies of the order of 0.1[Hz]. The motion of this oscillator is approximately planar, like the classical Foucault pendulum, and will have the same Foucault precession rate. The construction of a low frequency demonstrator is underway and will be followed by quantitative measurements which will examine both the Foucault effect as well as parasitic precession.

Modelling, Analysis, and Simulation of the Micro-Doppler Effect in Wideband Indoor Channels with Confirmation Through Pendulum Experiments

This paper is about designing a 3D no n-stationary wideband indoor channel model for radio-frequency sensing. The proposed channel model allows for simulating the time-variant (TV) characteristics of the received signal of indoor channel in the presence of a moving object. The moving object is modelled by a point scatterer which travels along a trajectory. The trajectory is described by the object’s TV speed, TV horizontal angle of motion, and TV vertical angle of motion. An expression of the TV Doppler frequency caused by the moving scatterer is derived. Furthermore, an expression of the TV complex channel transfer function (CTF) of the received signal is provided, which accounts for the influence of a moving object and fixed objects, such as walls, ceiling, and furniture. An approximate analytical solution of the spectrogram of the CTF is derived. The proposed channel model is confirmed by measurements obtained from a pendulum experiment. In the pendulum experiment, the trajectory of the pendulum has been measured by using an inertial-measurement unit (IMU) and simultaneously collecting CSI data. For validation, we have compared the spectrogram of the proposed channel model fed with IMU data with the spectrogram characteristics of the measured CSI data. The proposed channel model paves the way towards designing simulation-based activity recognition systems.