Relativity of Electric and Magnetic Fields previous home next Michael Fowler, University of Virginia A Magnetic Puzzle… Suppose we have an infinitely long straight wire, having a charge density of electrons of coulombs per meter, all moving at speed to the right (recall typical speeds are centimeters per minute) and a neutralizing fixed background of positive charge, also of course coulombs per meter. The current in the wire has magnitude (and actually is flowing to the left, since the moving electrons carry negative charge). Suppose also that a positive charge is outside the wire, a distance from the axis, and this outside charge is moving at the same exact velocity as the electrons in the wire. What force does the positive charge feel? The wire is electrically neutral, since it contains equal densities of positive and negative charges, both uniformly distributed throughout the wire (the illustration above is of course schematic). However, since is moving, it will feel a magnetic force, so the force on the charge is of magnitude
Magnetismo El motor eléctrico. Un motor eléctrico es un aparato que transforma energía eléctrica en energía mecánica. Existen diferentes tipos de motores, pero de entre todos tal vez sean los llamados “motores de corriente continua” los que permiten ver de un modo más simple cómo obtener movimiento gracias al campo magnético creado por una corriente. El gráfico muestra de modo esquemático las partes principales de un motor de corriente continua. Esquema de un motor eléctrico. El elemento situado en el centro es la parte del motor que genera el movimiento. El electroimán recibe la corriente a través del contacto establecido entre las escobillas y el conmutador. Cuando la corriente pasa a lo largo del electroimán, sus polos son atraídos y repelidos por los polos del imán fijo, de modo que el rotor se moverá hasta que el polo norte del electroimán quede mirando al polo sur del imán permanente. Para más información sobre motores eléctricos pincha aquí.
Personal and Historical Perspectives of Hans Bethe MAKE HOMEMADE SCIENCE TOYS AND PROJECTS El sueño del movimiento perpetuo | SETI Escrito por Prof. Alberto Unapiedra Los inventores de todas las épocas han intentado reiteradas veces crear lo que se llama una “máquina de movimiento perpetuo”. Ejemplo de una máquina de movimiento perpetuo. Una máquina de movimiento perpetuo no necesita energía externa para trabajar. La primera mención que se conoce a uno de estos artefactos corresponde al matemático y astrónomo hindú Báskara, aproximadamente en el año 1160. Leonardo Da Vinci y sus diseños para elevar agua. Para aclarar los conceptos repasemos primero dos principios básicos de la termodinámica: la conservación de la energía y la entropía. Perpetuum mobile 2Ilustración de Mariela Ba Existen dos tipos de máquinas de movimiento perpetuo: las que contradicen el primer principio o de primera especie y las que contradicen el segundo o de segunda especie. Perpetuum mobile 1Ilustración de Mariela Ba Category: Astronomia
An Essay by Einstein -- The World As I See It "How strange is the lot of us mortals! Each of us is here for a brief sojourn; for what purpose he knows not, though he sometimes thinks he senses it. But without deeper reflection one knows from daily life that one exists for other people -- first of all for those upon whose smiles and well-being our own happiness is wholly dependent, and then for the many, unknown to us, to whose destinies we are bound by the ties of sympathy. A hundred times every day I remind myself that my inner and outer life are based on the labors of other men, living and dead, and that I must exert myself in order to give in the same measure as I have received and am still receiving... "I have never looked upon ease and happiness as ends in themselves -- this critical basis I call the ideal of a pigsty. "My passionate sense of social justice and social responsibility has always contrasted oddly with my pronounced lack of need for direct contact with other human beings and human communities.
Sonoluminescence Single-bubble sonoluminescence - A single, cavitating bubble. Video of synthetic wound cavity collapsing creating sonoluminescence. Long exposure image of multi-bubble sonoluminescence created by a high-intensity ultrasonic horn immersed in a beaker of liquid History[edit] The sonoluminescence effect was first discovered at the University of Cologne in 1934 as a result of work on sonar. In 1989 an experimental advance was introduced by Felipe Gaitan and Lawrence Crum, who produced stable single-bubble sonoluminescence (SBSL). Properties[edit] Sonoluminescence can occur when a sound wave of sufficient intensity induces a gaseous cavity within a liquid to collapse quickly. Some facts about sonoluminescence: Rayleigh–Plesset equation[edit] The dynamics of the motion of the bubble is characterized to a first approximation by the Rayleigh-Plesset equation (named after Lord Rayleigh and Milton Plesset): Mechanism of phenomenon[edit] In 2002, M. Other proposals[edit] Quantum explanations[edit] [edit]
Einstein for Everyone Einstein for Everyone Nullarbor Press 2007revisions 2008, 2010, 2011, 2012, 2013 Copyright 2007, 2008, 2010, 2011, 2012, 2013 John D. Norton Published by Nullarbor Press, 500 Fifth Avenue, Pittsburgh, Pennsylvania 15260 with offices in Liberty Ave., Pittsburgh, Pennsylvania, 15222 All Rights Reserved John D. An advanced sequel is planned in this series:Einstein for Almost Everyone 2 4 6 8 9 7 5 3 1 ePrinted in the United States of America no trees were harmed web*bookTM This book is a continuing work in progress. January 1, 2015. Preface For over a decade I have taught an introductory, undergraduate class, "Einstein for Everyone," at the University of Pittsburgh to anyone interested enough to walk through door. With each new offering of the course, I had the chance to find out what content worked and which of my ever so clever pedagogical inventions were failures. At the same time, my lecture notes have evolved. This text owes a lot to many. i i i
Brief Answers to Cosmic Questions Structure of the Universe Does the Universe have an edge, beyond which there is nothing? Are the galaxies arranged on the surface of a sphere? Why can't we see the whole universe? Evolution of the Universe Did the Universe expand from a point? More about the Big Bang When they say "the universe is expanding," what exactly is expanding? Structure of the Universe Does the Universe have an edge, beyond which there is nothing? Are the galaxies arranged on the surface of a sphere? Why can't we see the whole universe? If you could suddenly freeze time everywhere in the universe, and magically survey all of creation, you would find galaxies extending out far beyond what we can see today. Does the term "universe" refer to space, or to the matter in it, or to both? Today, the situation is reversed. Discovering the properties of space remains one of the deepest and most important problems in modern science. Evolution of the Universe Did the Universe expand from a point? More about the Big Bang
100 Incredible Lectures from the World's Top Scientists Posted on Thursday June 18, 2009 by Staff Writers By Sarah Russel Unless you’re enrolled at one of the best online colleges or are an elite member of the science and engineering inner circle, you’re probably left out of most of the exciting research explored by the world’s greatest scientists. But thanks to the Internet and the generosity of many universities and online colleges, you’ve now got access to the cutting edge theories and projects that are changing the world in this list below. If you’re looking for even more amazing lectures, check out our updated list for 2012 with more talks from great minds. General Let the world’s top scientists explain exactly how they do their job when you listen to these lectures. Science and Engineering From materials science to the study of thermodynamics, learn more about the science of engineering here. WTC Lecture – collapse of WTC Buildings: Steven E. Biology and Medicine Chemistry Physics and Astronomy Earth and Environment Technology Science and Business