OPAC - Pencarian Artikel Jurnal & Majalah Library USD
Menampilkan semua artikel (Halaman 595 dari 34170, Total: 341698 data)
Eddy currents in multilayer coils
klik untuk membaca file PDF
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 284-290 |
| Abstrak | : | This article considers an example of eddy current behaviour that has not been described previously in textbooks and physics education journals. This phenomenon involves a sharp rise in the active resistance of a multilayer coil with increasing alternating current frequency. This effect is not explained by the classic skin effect and is not related to losses in a core. The results of measurements of the frequency dependence of the active resistance of multilayer coils obtained by the resonance method and the results of calculating this dependence in the framework of the tape model of a multilayer solenoid are presented. The special case of relatively low frequencies is analysed when the classic skin effect is weak in a solitary wire. However, the active resistance of a multilayer coil is significantly higher than its DC resistance. A schematic model of the observed effect is proposed. The analysed example of eddy currents is easy to realize in an experiment and open to clear physical interpretation. It might be appropriate for students of various specialities to discuss this effect in intermediate or advanced physics laboratories. |
Resolving tensions surrounding massive pulleys
| Pengarang | : | D. J. Durian |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 277-283 |
| Abstrak | : | The distribution of string tension on the contact line between an ideal string and a massive pulley is a frequently discussed but incompletely posed problem that confronts students in introductory mechanics. We highlight ambiguities in the usual presentation of this problem by the massive Atwood's machine and discuss two compact resolutions that treat situations where the pulley or the string elastically deforms. We propose experiments that can be developed in an intermediate laboratory to determine the tension profile. |
Understanding and enhancing the impact-induced tension of a falling chain
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 267-276 |
| Abstrak | : | When a falling chain strikes a surface, it can accelerate downwards faster than free-fall. This counterintuitive effect occurs when a tension is created in the chain above where it strikes the surface. The size of this tension, and how it is produced, depend on the type of chain used. For a chain made of rods that are slightly tilted from horizontal, the impact-induced tension is readily observable. Here are reported experimental observations on such a falling chain for two different situations: when the chain strikes an inclined surface, and when the chain's mass density decreases with height. It is found that both of these arrangements can increase the downward acceleration. To quantitatively describe these observations, a theoretical model is developed. The model successfully predicts the chain's position and velocity, even when the top end approaches the surface, without any free parameters. The model also predicts that uniform rods are practically the best for producing large tensions. |
Mechanical approach to surface tension and capillary phenomena
| Pengarang | : | Marc Durand |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 261-266 |
| Abstrak | : | Many textbooks dealing with surface tension favor the thermodynamic approach (minimization of some thermodynamic potential such as free energy) over the mechanical approach (balance of forces) to describe capillary phenomena, stating that the latter is flawed and misleading. Yet, a mechanical approach is more intuitive for students than free energy minimization, and does not require any knowledge of thermodynamics. In this paper, we show that capillary phenomena can be correctly described using the mechanical approach, as long as the system on which the forces act is properly defined. After reviewing the microscopic origin of a tangential tensile force at the interface, we derive the Young–Dupré equation, emphasizing that this relation should be interpreted as an interface condition at the contact line, rather than a force balance equation. This correct interpretation avoids misidentification of capillary forces acting on a given system. Moreover, we show that a reliable method to correctly identify the acting forces is to define a control volume that does not embed any contact line on its surface. Finally, as an illustration of this method, we apply the mechanical approach in a variety of ways on a classic example: the derivation of the equilibrium height of capillary rise (Jurin's law). |
High-speed visualization of soap films bursting dynamics
| Pengarang | : | Arseny A. Volodko |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 253-260 |
| Abstrak | : | High-speed (2873 fps) visualization of soap film bursting dynamics has been performed by means of equipment available to a high school laboratory. This paper presents the geometry of the experiment and description of the analysis method of the video frames. We carried out the experiments on the bursting of vertical plane soap films using a circular frame with single central and non-central puncture of the film by a needle. The studies were also performed with simultaneous puncture of the film by two needles. Similar research of the films bursting was done using a non-circular frame in the form of a nonconvex hexagon. In all cases, the rupture line has the shape of a circle. For the first time, the displacement of the circular burst center upwards is recorded and explained. Flapping oscillations of the rupture line border at its movement are confirmed. The oscillating character of the rupture line movement is recorded and explained. In addition, we detected formation of the liquid bridge and its destruction at the interaction of two circular bursts with double puncture of the film. |
Different scenarios of shrinking surface soap bubbles
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 244-252 |
| Abstrak | : | We discuss a simple experiment investigating the shrinkage of surface soap bubbles sitting on a thin solid plate with a circular orifice located under the apex of the bubble. We identify three different shrinking regimes, the occurrence of which depends on a combination of key parameters that include the ratio between initial bubble and orifice sizes and physicochemical properties of the fluid system. For low-viscosity liquids and/or large ratios, a bubble remains quasi-hemispherical as shrinking proceeds. In contrast, for liquids with sufficiently large viscosities and/or small geometric ratios, a bubble seeks the shape of a spherical cap while the air inside it escapes through the orifice. In this case, shrinking proceeds with a bubble foot that either recedes over time or does not move for the largest viscosities and/or smallest ratios. We use basic physical arguments to rationalize the three identified regimes and to explain the shrinking dynamics. Specifically, this model which captures observations and measurements is based on Bernoulli's principle for the air flow, volume conservation, and a friction law that accounts for viscous dissipation at the moving bubble foot. |
The sun diver: Combining solar sails with the Oberth effect
| Pengarang | : | Coryn A. L. Bailer-Jones |
| Nama Majalah/Jurnal | : | American Journal of Physics |
| Volume / Edisi | : | 89 (No. 3) |
| Halaman | : | 235-243 |
| Abstrak | : | A highly reflective sail provides a way to propel a spacecraft out of the solar system using solar radiation pressure. The closer the spacecraft is to the Sun when it starts its outward journey, the larger the radiation pressure and so the larger the final velocity. For a spacecraft starting on the Earth's orbit, closer proximity can be achieved via a retrograde impulse from a rocket engine. The sail is then deployed at the closest approach to the Sun. Employing the so-called Oberth effect, a second, prograde, impulse at closest approach will raise the final velocity further. Here, I investigate how a fixed total impulse (? Δ??) can best be distributed in this procedure to maximize the sail's velocity at infinity. Once Δ? exceeds a threshold that depends on the lightness number of the sail (a measure of its sun-induced acceleration), the best strategy is to use all of the Δ? in the retrograde impulse to dive as close as possible to the Sun. Below the threshold, the best strategy is to use all of the Δ? in the prograde impulse and thus not to dive at all. Although larger velocities can be achieved with multi-stage impulsive transfers, this study shows some interesting and perhaps counter-intuitive consequences of combining impulses with solar sails. |
EFEKTIVITAS PEMANFAATAN DANA APP DI PAROKI SANTO YOHANES RASUL WONOGIRI TAHUN 2010-2011
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Orientasi Baru: Jurnal Filsafat dan Teologi |
| Volume / Edisi | : | 25 (No. 1) |
| Halaman | : | 37-56 |
| Abstrak | : | Fast becomes one of the expressions of penance from the Chris tians during the Lent. Fast is an effort of mortification. Aksi Puasa Pembangunan (APP) is an act of fast in the form of alms. Through the APP, the penance is directed to build His Kingdom (compared to LG art 1). In this case, the Kingdom of God is not created by human, but it is by God. Human only participates in the process, and prepare His coming until He comes and give the fulfilment. Vision of “constructing” in APP is based on the self-renewal which give birth the social renewal in the society. In the period of construction, fast is directed to the actions which can lead human to his entity. APP movement enable the development of Christians to be more responsible for his own life and the society |
GUTIERREZ DAN TEOLOGI PEMBEBASAN
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Orientasi Baru: Jurnal Filsafat dan Teologi |
| Volume / Edisi | : | 25 (No. 1) |
| Halaman | : | 19-36 |
| Abstrak | : | Liberation theology emerges as a movement within the Chatolic Church in Latin America in the 1950s and 1960s. This movement is principally as a moral reaction to the poverty and social injustice in the region. Gustavo Guttiérrez gives the movement its name: “theology of liberation” (1971) that attempts to interpret Scripture through the plight of the poor. This essay deals with the Guttiérrez concept of theology of liberation. From Gutiérrez, we learn that doing theology means to seek to interpret the actions of the Catholic Church and the teachings of Jesus Christ from the perspective of the poor and disadvantaged. |
PENGHAYATAN EKARISTI UMAT PAROKI SANTO YOHANES RASUL SOMOHITAN MENURUT KEVIN W. IRWIN
| Pengarang | : | FR. Marcellinus Roselawanto |
| Nama Majalah/Jurnal | : | Orientasi Baru: Jurnal Filsafat dan Teologi |
| Volume / Edisi | : | 25 (No. 1) |
| Halaman | : | 1-18 |
| Abstrak | : | The faithful of the Archdiocese of Semarang put a high respect on the Eucharist in their daily life. In many parishes, there are so many people who celebrate and participate in the Eucharist. Besides, they also try to understand and fully experience the Eucharist in their daily life among others. This research, concludes that the Eucharist as the expression of the faith was fully experienced by the people of Santo Yohanes Rasul Somohitan Parish. It was supported by many kinds of means and by the proper understanding of the Eucharist. The Eucharist also gave the positive influences to the personal growth and the sensitivity of the social situations. This research showed that there was a close relationship between lex orandi, lex credendi, and lex vivendi. What the people pray, is what people be lieve in, and what the people believe in, is what the people fully experience. The Eucharist’s full and comprehension in Santo Yo hanes Rasul Somohitan parish should be evaluated continuesly. Based on that discovery, the Church was expected to give cathecism and other activities which could improve the Eucharist’s full and comprehension. And could give more positive influences to the community life. |