O movimento harmônico simples de um sistema massa-mola geralmente mostra um comportamento que é fortemente determinado pelos parâmetros geométricos da mola. Neste trabalho estuda-se o comportamento oscilatório de um sistema massa-mola considerando o efeito da variação do valor médio do diâmetro Φ da mola na constante elástica k, a frequência angular ω, o fator de amortecimento γ e a dinâmica das oscilações. Nós encontramos que a constante elástica k é proporcional a Φ- 3, enquanto a frequência ω0 é proporcional a Φ- 3 / 2, e que γ diminui quando Φ aumenta. Também se mostram as diferenças encontradas no valor da frequência angular ω quando as molas são consideradas ideais (sem massa), levando em conta a massa efetiva da mola, e levando em conta o amortecimento das oscilações. Esta experiência oferece aos estudantes a possibilidade de compreender as diferenças nos modelos teóricos que levam em conta correções que são bem conhecidas para determinar a frequência das oscilações de um sistema massa-mola.

The simple harmonic motion of a spring-mass system generally exhibits a behavior strongly influenced by the geometric parameters of the spring. In this paper, we study the oscillatory behavior of a spring-mass system, considering the influence of varying the average spring diameter Φ on the elastic constant k, the angular frequency ω, the damping factor γ, and the dynamics of the oscillations. It was found that the elastic constant k is proportional to Φ-3, while the natural frequency ω0 is proportional to Φ- 3 / 2, and γ decreases as Φ increases. We also show the differences obtained in the value of the angular frequency ω when the springs are considered as ideal (massless), taking into account the effective mass of the spring, and considering the influence of the damping of the oscillations. This experiment provides students with the possibility of understanding the differences between theoretical models that include well-known corrections to determine the frequency of oscillations of a spring-mass system.

In this paper a study of the sound transmission loss (PT) in various everyday materials such as styrofoam, cardboard, glass, cotton and sisal is performed. The experimental setup consists of two sound level meters and an absorbing anechoic chamber. It is shown in detail how to build with inexpensive materials the anechoic chamber used to measure the PT. From the difference in the nominal measures of the two sound level meters located inside the anechoic chamber the PT data are recorded. With the PT data as a function of frequency and sweeping the frequency spectrum in third octave bands from 100 Hz to 5.000 Hz, the different curves that characterize the materials acoustic behavior are plotted. We show the PT dependence with the density and structure of the material used to attenuate the sound. This experiment can be used in physics or engineering courses, like waves or materials characterization, for students to explore the sound insulation capability of a wide variety of materials readily available in their environment.

En este trabajo se realiza un estudio de la pérdida de transmisión sonora (PT) en diversos materiales de uso cotidiano, tales como: icopor, cartón, vidrio, algodón y fique. El montaje experimental consta básicamente de dos sonómetros y una cámara anecoica absorbente. Se muestra en detalle la construcción de la cámara anecoica utilizada para medir la PT, empleando materiales de bajo costo. Calculando la diferencia de las medidas nominales en los dos sonómetros ubicados dentro de la cámara anecoica se registran los datos de PT. Con los datos de PT en función de la frecuencia y barriendo un espectro en bandas de tercio de octava desde los 100 Hz hasta 5.000 Hz, se grafican distintas curvas que caracterizan el comportamiento acústico de los materiales estudiados. Se muestra la dependencia de la PT con la densidad y la estructura del material empleado para atenuar el sonido. Este experimento puede ser utilizado en cursos de física o ingeniería, como el de ondas o caracterización de materiales, para que los estudiantes exploren la capacidad de aislamiento sonoro de una gran diversidad de materiales disponibles fácilmente en su entorno.

Single phase ?-Al2O3 ceramic foams with high surface area (~180 m²/g) and porosity (67%) were prepared by the polyurethane sponge method from slurries containing ?-Al2O3 (~40 wt % of solids). Different commercial polyurethane sponges were tested as templates for the ceramic foams, and the better results were obtained with a hydrophilated polyester polyurethane with pore density of 122 ppi, and thermal behavior that suggested the presence of fire retardant and smoke suppressor additives. The mechanical strength of the ceramic foams depended on several factors, such as the chemical nature of the sponge employed as template, composition of the slurry, and the heating rate during calcination. It was found that at least four cycles of re-coating followed by drying were required before calcination to prevent collapse of the ceramic foams.

The phenomenon of temperature distribution in a rotating gas flow is known as the Ranque-Hilsch effect. The Ranque-Hilsch tube (R-H ) is a system that in absence of movable parts separates an air flow in two portions, cold and hot ones. In this work a R-H tube is constructed using low cost pieces. We showed that effect is dependent of some of its parameters like the: tube length, the exit diameter of cold air and the diameter of a cylindrical valve in the temperature gradient generated at its ends. As result a configuration of the tube is obtained that optimizes the temperature difference of the flow. The R-H tube is constructed with materials of low cost and easy to obtain, which facilitates its assembly in order to illustrate some phenomena in fluid mechanics and thermodynamics labs in engineering and physics courses.

El fenómeno de distribución de temperatura en un flujo de gas rotante es conocido como el efecto Ranque-Hilsch. El tubo Ranque-Hilsch (R-H) es un sistema que en ausencia de partes móviles separa un flujo de aire en dos porciones, fría y caliente. En este trabajo un tubo R-H es construido utilizando piezas de bajo costo. Nosotros mostramos el efecto que tiene variar algunos de sus parámetros como: la longitud del tubo, el diámetro de salida de aire frío y el diámetro de una válvula cilíndrica en el gradiente de temperatura generado en los extremos. Como resultado se obtiene una configuración del tubo que optimiza la diferencia de temperatura del flujo. El tubo R-H es construido con materiales de bajo costo y fáciles de conseguir, lo cual facilita su montaje para ilustrar fenómenos de fluidos en los laboratorios de mecánica de fluidos y termodinámica en las carreras de ingeniería y física.

The beams deflection is an important subject in physics and engineering courses to study the elastic properties of a great variety of industrial materials . In this work the experimental deflection of thin glass sheets in cantilever is presented. The deflection test is realized putting weights on the free extreme of glass sheets, in order to determine the dependence of elastic properties and breaking point with length and width of the beams. The material is also examined to verified if presents mechanical hysteresis. Finally a comparison between the experimental elastic curve and the calculated whit the small slopes model is performed. This is a very cheap experiment which could be implemented easily in physics or engineering labs to illustrate materials elastic properties.

La flexión de vigas es una importante área en los cursos de física e ingeniería para el estudio de las propiedades elásticas de una gran variedad de materiales que se emplean en la industria. En el presente trabajo se realiza un experimento de la flexión de láminas delgadas de vidrio en voladizo, sometiéndolas a un ensayo de flexión por medio de masas que se colocan en el extremo libre. Lo anterior con el fin de determinar hasta que grado el material es elástico y observar la dependencia del punto de fractura con la longitud y el ancho de la lámina de vidrio. Se examina si el material presenta histéresis mecánica. Finalmente se compara la curva experimental de la elástica con la calculada a partir del modelo de pequeñas pendientes. Este es un experimento de muy bajo costo, que puede ser implementado fácilmente en los laboratorios de física o de ingeniería para ilustrar las propiedades elásticas de materiales.

Mercuric Iodide (HgI2) is a semiconductor candidate for the construction of X- and gamma-ray detectors for digital medical imaging due to its high atomic number (Z Hg = 80, Z I = 53). Also, HgI2 has a wide optical band-gap (2.13 eV) and high photon absorption coefficient for high-energy radiation. Different structures can lead to varying electrical and optical properties of the final material. In this work, HgI2 crystals were produced by the solvent evaporation technique. The solvents used were ethanol (solubility around 20 mg/ml at 25ºC), ether (solubility around 3.5 mg/ml at 25ºC) and acetone (solubility around 24mg/ml at 25ºC). The evaporation conditions were varied in order to produce different final crystals. The Bérnard cells are responsible for crystallites formation due to the Bérnard-Maragoni convection in the liquid. Millimeter-sized crystals can be obtained as seen by Scanning Electron Microscopy.

A density oscillator or saline oscillator is a nonlinear system. It presents alternating changes on the direction of time flow, as effect of the space restrictions between two flows of different densities. The fluids are contained in different vessels interconnected by a vertical capillary. In this work a density oscillator is constructed, and the oscillation is studied in function of some parameters. Those parameters are the concentration of the electrolyte salt (NaCl) and the length of the capillary tube. In order to measure the variation parameters effect, an aluminum electrode is placed in each solution and the electrical potential signal is registered with a digital multimeter. The variation of electrical potential allows us to observe how the flow direction evolves with time for the density oscillator. The analysis was made by interpretation of the electrical potential signal as function of time. We found phenomenological relationships between the oscillation period and the difference of the peak-to-peak potential in function of some experimental parameters, like: salt concentration and length of the capillary tube.

Un oscilador de densidad u oscilador salino, es un sistema no lineal que presenta cambios alternantes del sentido de flujo en el tiempo, como efecto de las restricciones espaciales entre dos fluidos de diferente densidad. Los fluidos están en recipientes separados, los cuales están interconectados por medio de un tubo capilar vertical. En este trabajo se construye un oscilador de densidad para estudiar la influencia de la variación de algunos de sus parámetros sobre las oscilaciones en el sentido de flujo. Sean dichos parámetros, la concentración de la sal (NaCl) del electrólito y la longitud del capilar. Para medir el efecto de la variación de los parámetros, se coloca un electrodo de aluminio en cada una de las soluciones y la señal de potencial eléctrico es registrada mediante un multímetro digital, lo que permite observar como evoluciona temporalmente la inversión en el sentido de flujo del oscilador de densidad. El análisis se efectuó mediante la interpretación gráfica de las series de potencial eléctrico en función del tiempo, encontrando relaciones fenomenológicas entre el período de oscilación y la diferencia de potencial pico a pico respecto a los parámetros experimentales: concentración de la sal y longitud del capilar.