Notas detalladas sobre Perpetual Marble Machine Kinetic
Notas detalladas sobre Perpetual Marble Machine Kinetic
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The principles of thermodynamics are so well established, both theoretically and experimentally, that proposals for perpetual motion machines are universally dismissed by physicists. Any proposed perpetual motion design offers a potentially instructive challenge to physicists: one is certain that it cannot work, so one must explain how it fails to work. The difficulty (and the value) of such an exercise depends on the subtlety of the proposal; the best ones tend to arise from physicists' own thought experiments and often shed light upon certain aspects of physics.
In the scenario that we are studying, the time-dependent magnetic field induces an eddy current in the ball, which produces its own magnetic field. Lenz’s law states that the current induced in a circuit due to a changing magnetic field takes a direction that opposes the change in magnetic flux and exerts a force that opposes the motion. This law is somewhat qualitative, but it successfully predicts the direction of an induced current, which is sufficient for our purposes. Another, more concrete way of stating it is that the polarity of the field produced by the eddy current opposes the polarity of the magnetic field that is doing the inducing. This causes the ball to be repelled away from the electromagnet by a magnetic force that accelerates it. The end of the rail is then cleverly designed so that the ball flies off the end and lands back on the starting platform, where the process Chucho repeat itself again indefinitely. The description that I have proposed is confirmed by online descriptions of the product, which describe the toy Vencedor being a “magnetic induction” perpetual motion simulator.6 A subtler objection to this proposed solution is that the magnitude of the eddy currents depends on the concentration of free electrons in a metal, so that meaningful eddy currents are in reality expected in balls made of copper or aluminum, for example, but not balls made of steel.
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6. The device can be bought online for around a hundred dollars, which seems like a reasonable price for a toy that will be used many times in demonstrations to illustrate physical principles.6 The main benefit of having a version of the device in class is that students Chucho study its motion up close and obtain video images. An exercise that I would suggest is to create a montage of the toy by superimposing between 10 and 20 balls at their locations over the course of one cycle. For example, if T
The electric field produced by a stationary set of charges is conservative, but in this case, the effect of the electric field is equivalent to that of a (nonconservative) magnetic field (i.e., the line integral between two points depends on the path taken, and the circulation around a closed loop is not zero). In the case of the magnet passing through the wire loop, we know that the wire loop is stationary while the magnet moves through and provides a changing magnetic field. A current is produced, so an EMF (electromotive force) must be driving it. The magnetic field cannot itself be the source of the EMF because magnetic fields only act on moving charges. Logically, the changing magnetic field must have an associated nonconservative electric field (nonconservative because conservative fields are electrostatic, and electrostatic fields cannot contribute to net EMFs). The induced EMF around a closed curve is the same Figura the voltage drop (i.e., the same Vencedor the line integral of the electric field around that curve). Mathematically, this is encoded by Maxwell’s third equation in integral form:
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However, the material used for the balls is described in the online product description only as “metal” rather than stainless steel, whereas the rails are explicitly described Ganador being made of “stainless steel.”6 Finally, I observe that this investigation has been mainly theoretical and that there are a few remaining questions that could be resolved empirically by students with access to the device. The motion of the ball and the way it “jumps” due to Lenz’s law is quite similar to a classic demonstration known as Thomson’s jumping ring, where an aluminum or copper ring is placed on the end of an electromagnet. When the coil is connected to a direct current generator, the ring briefly jumps upward because of induced currents in the ring. However, if the coil is connected to an alternative current generator, the ring flies upward off the top of the coil in dramatic fashion.8,9 Explaining why an AC current has this effect is not an easy exercise.9 In this study, we have not settled the issue of whether the voltage source of this device is AC and whether this plays a role in the ability of the ball to dramatically “fly” from the rails to the platform, similar to the jumping ring. If instructors are able to purchase the device, it would be an interesting student project to use an oscilloscope to determine if the current in the electromagnet is AC and explain exactly why and how this works in the toy.
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The history of perpetual motion machines dates back to the Middle Ages.[13] For millennia, it was not clear whether perpetual motion devices were possible or not, until the development of modern theories of thermodynamics showed that they were impossible.
A more thorough analysis showed that when a physical ratchet was considered at this molecular scale, Brownian motion would also affect the ratchet and cause it to randomly fail resulting in no net gain. Thus, the device would not violate the laws of thermodynamics.
The drinking bird toy functions using small ambient temperature gradients and evaporation. It runs until all water is evaporated.