Marcos H. Giménez

Using a mobile phone acceleration sensor in physics experiments on free and damped harmonic oscillations

We have used a mobile phone acceleration sensor, and the Accelerometer Monitor application for Android, to collect data in physics experiments on free and damped oscillations. Results for the period, frequency, spring constant, and damping constant agree very well with measurements obtained by other methods. These widely available sensors are likely to find increased use in instructional laboratories.

Measuring coupled oscillations using an automated video analysis technique based on image recognition

The applications of the digital video image to the investigation of physical phenomena have increased enormously in recent years. The advances in computer technology and image recognition techniques allow the analysis of more complex problems. In this work, we study the movement of a damped coupled oscillation system. The motion is considered as a linear combination of two normal modes, i.e. the symmetric and antisymmetric modes. The image of the experiment is recorded with a video camera and analysed by means of software developed in our laboratory. The results show a very good agreement with the theory.

Contribution of digital simulation in visualizing physics processes

In our experience of teaching physics for engineering at university level we have learned that the mathematical relationships between the parameters that control a process are important, but not sufficient, to understand a process. Such knowledge will only be consolidated if the new concept is incorporated by student in his field of study. Simulation programs, especially through visualization, can help to attain this target. We have developed three programs using Visual Basic. One of them is devoted to fitting experimental data and is complementary to experimental work; the others focus on dynamics, translation, and rotational movement, helping to understand the Newtons laws.

Using image recognition to automate video analysis of physical processes

Multimedia technologies and video analysis allow the design of low-cost physical measurement and data acquisition systems. The number of pixels in the images limits their spatial resolution, whereas their time resolution depends on the number of frames recorded per second. Both characteristics are determined by the video recording system used. We have developed a laboratory system with these characteristics where important improvements have been reached by using image recognition to automate video analysis. In the present work we first examine several image recognition techniques and evaluate them from the point of view of their application to measurement systems. Then we describe the proposed system and the methodology followed in the measurement process. An image of an experimental object is recorded and used as a filter, while the sequence of images of that object in motion become the input frames for the recognition process. Finally, we discuss the results obtained by this measurement process and comp...

Digital simulation of wave motion

Information and communication technologies have been shown to be very effective in the transmission of scientific knowledge. Nowadays, the development of software and hardware makes it possible to simulate processes as close to reality as we want. However, when we are trying to explain some complex physical processes, it is better to simplify the problem by means of simplified pictures of the total process. In the present work, we analyze the design of a simulation program of wave motion developed in our laboratory. The aim of the program is to help students to understand the basic concepts of the wave motion. For this reason, we have paid special attention to interactivity and graphic aspects.

Testing Theoretical Models of Magnetic Damping Using an Air Track.

Magnetic braking is a long-established application of Lenzs law. A rigorous analysis of the laws governing this problem involves solving Maxwells equations in a time-dependent situation. Approximate models have been developed to describe different experimental results related to this phenomenon. In this paper we present a new method for the analysis of magnetic braking using a magnet fixed to the glider of an air track. The forces acting on the glider, a result of the eddy currents, can be easily observed and measured. As a consequence of the air track inclination, the glider accelerates at the beginning, although it asymptotically tends towards a uniform rectilinear movement characterized by a terminal speed. This speed depends on the interaction between the magnetic field and the conductivity properties of the air track. Compared with previous related approaches, in our experimental setup the magnet fixed to the glider produces a magnetic braking force which acts continuously, rather than over a short period of time. The experimental results satisfactorily concur with the theoretical models adapted to this configuration.

Undergraduate experiment with fractal diffraction gratings

We present a simple diffraction experiment with fractal gratings based on the triadic Cantor set. Diffraction by fractals is proposed as a motivating strategy for students of optics in the potential applications of optical processing. Fraunhofer diffraction patterns are obtained using standard equipment present in most undergraduate physics laboratories and compared with those obtained with conventional periodic gratings. It is shown that fractal gratings produce self-similar diffraction patterns which can be evaluated analytically. Good agreement is obtained between experimental and numerical results.

FALSE WAVES IN WAVE RECORDS AND NUMERICAL SIMULATIONS

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

CONDITIONAL SIMULATIONS IN LABORATORY FLUMES

Tanah Lot Temple is situated in Tabanan Regency - Bali, on the coast of the Indonesian Ocean. Due to continuous wave attack, wind force, and weathering of the rock bank where the Temple stands, abrasion has occured which is more and more threatening the existence of the Temple. Considering that Tanah Lot Temple is a sacred place for the Hindu Balinese people and a place of high cultural value, and also an important tourism, steps to save the Temple are imperative. The Central as well as the Regional Authorities, and also the Bali nese community are very much interested in the effort to keep the Temple intact. Measures have been undertaken to protect both the seaside and land-side banks of the Temple rock bank. This paper only discusses counter measures of the sea —side bank of the Temple.

Direct Visualization of Mechanical Beats by Means of an Oscillating Smartphone

The resonance phenomenon is widely known in physics courses. Qualitatively speaking, resonance takes place in a driven oscillating system whenever the frequency approaches the natural frequency, resulting in maximal oscillatory amplitude. Very closely related to resonance is the phenomenon of mechanical beating, which occurs when the driving and natural frequencies of the system are slightly different. The frequency of the beat is just the difference of the natural and driving frequencies. Beats are very familiar in acoustic systems. There are several works in this journal on visualizing the beats in acoustic systems. For instance, the microphone and the speaker of two mobile devices were used in previous work to analyze the acoustic beats produced by two signals of close frequencies. The formation of beats can also be visualized in mechanical systems, such as a mass-spring system or a double-driven string. Here, the mechanical beats in a smartphone-spring system are directly visualized in a simple way. T...