Perpetual motion
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Perpetual motion refers to a condition in which an object continues to move indefinitely without being driven by an external source of energy. In effect by its very definition, Perpetual Motion is a system wherein the item in question consumes and outputs at least 100% of its energy constantly, sustaining no net loss as a result of the laws of thermodynamics. Using modern terminology, any machine that purports to produce more energy than it uses is a "perpetual motion machine", although somewhat oddly named as they may not include any moving parts.
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[edit] Basic principles
Perpetual motion machines violate one or both of the following two laws of physics: the first law of thermodynamics and the second law of thermodynamics. The first law of thermodynamics is essentially a statement of conservation of energy. The second law has several statements, the most intuitive of which is that heat flows spontaneously from hotter to colder places; the most well known is that entropy tends to increase, or at the least stays the same; another statement is that no heat engine (an engine which produces work while moving heat between two places) can be more efficient than a Carnot heat engine. As a special case of this, any machine operating in a closed cycle cannot only transform thermal energy to work in a region of constant temperature.
Machines which are claimed not to violate either of the two laws of thermodynamics but rather are claimed to generate energy from unconventional sources are sometimes referred to as perpetual motion machines, although they do not meet the standard criteria for the name. By way of example, it is quite possible to design a clock or other low-power machine to run on the differences in barometric pressure or temperature between night and day [1]. Such a machine has a source of energy, albeit one from which it is quite impractical to produce power in quantity.
[edit] Classification
It is customary to classify perpetual motion machines as follows:
- A perpetual motion machine of the first kind produces strictly more energy than it uses, thus violating the law of conservation of energy. Over-unity devices, that is, devices with a thermodynamic efficiency greater than 1.0 (unity, or 100%), are perpetual motion machines of this kind.
- A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. This need not violate the law of conservation of energy, since the thermal energy may be equivalent to the work done; however it does violate the more subtle second law of thermodynamics (see also entropy). Note that such a machine is different from real heat engines (such as car engines), which always involve a transfer of heat from a hotter reservoir to a colder one, the latter being warmed up in the process. The signature of a perpetual motion machine of the second kind is that there is only one single heat reservoir involved, which is being spontaneously cooled without involving a transfer of heat to a cooler reservoir. This conversion of heat into useful work, without any side effect, is impossible by the second law of thermodynamics.
In an otherwise completely empty Newtonian universe, a single particle could travel forever at constant velocity with no violation of the laws of physics – though of course no energy could be extracted from it without slowing it down. For example, an electron can spin around a nucleus in an atom of matter indefinitely unless it or the atom is disrupted in some way. Similarly, in an isolated system consisting of two objects orbiting each other gravitationally, the two objects will remain in orbiting motion forever, as long as they are not disturbed, assuming however, if the two orbiting bodies are at a perfect distance that the moon is not sucked into the main body, via gravity, and does not spin away due to centripetal force. However any attempt to extract useful work from this system would lead to a loss of energy. This would result in the objects slowing down and getting closer to each other, until at some point the objects would collapse together and no more energy would remain to extract.
[edit] Use of the term "impossible" and perpetual motion
Scientists and engineers accept the possibility that the current understanding of the laws of physics may be incomplete or incorrect; a perpetual motion device may not be impossible, but overwhelming evidence would be required to justify rewriting the laws of physics.
The conservation laws are particularly robust. Noether's theorem is actually a proof that any conservation law can be derived from any continuous symmetry. In other words, as long as the laws of physics (not simply the current understanding of them, but the actual laws, which may still be undiscovered) and the various physical constants remain invariant over time, the conservation laws must be true.
Any proposed perpetual motion design offers a potentially instructive challenge to physicists: we know it can't work (because of the laws of thermodynamics), so 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. The principles of thermodynamics are so well established that proposals for perpetual motion machines are often met with disbelief on the part of physicists.
| “ | The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. | ” |
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- --Sir Arthur Stanley Eddington, The Nature of the Physical World (1927)
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[edit] Thought experiments
Serious work in theoretical physics often involves thought experiments that test the boundaries of understanding of physical laws. Some such thought experiments involve apparent perpetual motion machines, and insight may be had from understanding why they either don't work or don't violate the laws of physics. For example:
- Maxwell's demon: a thought experiment which led to physicists' considering the interaction between entropy and information
- Feynman's "Brownian ratchet": a "perpetual motion" machine which extracts work from thermal fluctuations and appears to run forever but only runs as long as the environment is warmer than the ratchet
- Self-perpetuating cosmic inflation: Andrei Linde has proposed that during the theoretical period of cosmic inflation in the early universe, quantum fluctuations in energy could be magnified by the very inflationary process, preventing the global cooling trend from ever being fully consummated. This would violate both the first and second laws of thermodynamics; indeed, it may constitute the origin of a low-entropy past that gets the second law going in the first place. However, a machine to harness this principle would have several serious flaws. It would need to use unimaginable amounts of energy (on at least a Planck scale); it might have cataclysmic consequences to the area around it for an unknown distance (there is no a priori natural limit to the scale of the damage); and at least the majority and possibly all the energy it generated would be in a newly-created universe which might be inaccessibly far away along a wormhole.
- Laser Elevator: Suppose we had a mechanism for converting mass into energy and back without any losses. Convert a measure of mass into light energy, beam it up into the sky, and convert it back into mass. Then, extract the energy liberated by the falling mass. The flaw here is that, by general relativity, the laser is red-shifted when ascending out of the gravity well, and the energy lost exactly equals the amount of energy that could be extracted from the falling mass.
[edit] Techniques
Some ideas recur repeatedly in perpetual motion machine designs. For instance:
The seemingly mysterious ability of magnets to influence motion at a distance without any apparent energy source has long appealed to inventors. However, a constant magnetic field does no work because the force it exerts on a charged particle is always at right angles to its motion; a changing field can do work, but requires energy to sustain. A "fixed" magnet can do work, but energy is dissipated in the process, typically weakening the magnet's strength over time. Thus, when a magnet does work by lifting an iron weight, potential energy is converted to kinetic energy. Once the iron hits the magnet its kinetic energy is converted to heat and sound. In order to release further energy, the iron must be moved away from the magnet. This converts the energy of your arm to potential energy again. Since the energy of parting the magnet and iron is identical to the energy released as the magnet and iron come together, no net energy can be gained by changing the iron - magnet distance.
Gravity also acts at a distance, without an apparent energy source. But to get energy out of a gravitational field (for instance, by dropping a heavy object, producing kinetic energy as it falls) you have to put energy in (for instance, by lifting the object up), and some energy is always dissipated in the process. A typical application of gravity in a perpetual motion machine is Bhaskara's wheel, whose key idea is itself a recurring theme, often called the overbalanced wheel: Moving weights are attached to a wheel in such a way that they fall to a position further from the wheel's center for one half of the wheel's rotation, and closer to the center for the other half. Since weights further from the center apply a greater torque, the result is (or would be, if such a device worked) that the wheel rotates forever. The moving weights may be hammers on pivoted arms, or rolling balls, or mercury in tubes; the principle is the same.
Gravity and magnetism are an attractive combination indeed, and a frequently rediscovered design has a ball pulled up by a magnetic field and then rolling down under the influence of gravity, in a cycle. (At the highest point, the ball is supposed to have acquired enough speed to escape the magnet's influence.)
To extract work from heat, thus producing a perpetual motion machine of the second kind, the most common approach (dating back at least to Maxwell's demon) is unidirectionality. Only molecules moving fast enough and in the right direction are allowed through the demon's trap door. In a Brownian ratchet, forces tending to turn the ratchet one way are able to do so while forces in the other direction aren't. A diode in a heat bath allows through currents in one direction and not the other. These schemes typically fail in two ways: either maintaining the unidirectionality costs energy (Maxwell's demon needs light to look at all those particles and see what they're doing), or the unidirectionality is an illusion and occasional big violations make up for the frequent small non-violations (the Brownian ratchet will be subject to internal Brownian forces and therefore will sometimes turn the wrong way).
[edit] New physics which would allow perpetual motion
- If hypothetical mirror matter exists, some Maxwell's demons can be made operational. Yet the Second Law is not violated because the demons pay their entropy cost in the hidden (mirror) sector of the world.
- Forms of pure energy (aka free energy) with no other relations of physics attached to it.
[edit] Invention history
The recorded history of perpetual motion machines dates at least as far back as the 8th century. Proponents of perpetual motion machines use a number of other terms to describe their inventions, including "free energy" and "over unity" machines. An early description of a perpetual motion machine was by Bhaskara in 1150. He described a wheel that he claimed would run forever. Villard de Honnecourt in 1235 described, in a thirty-three page manuscript, a perpetual motion machine of the second kind.
In 1775 Royal Academy of Sciences in Paris issued the statement that Academy "will no longer accept or deal with proposals concerning perpetual motion". Johann Bessler (also known as Orffyreus) created a series of claimed perpetual motion machines in the 18th Century. In the 19th century, the invention of perpetual motion machines became an obsession for many scientists. Many machines were designed based on electricity, but none of them lived up to their promises. Another early prospector in this field included John Gamgee. Gamgee developed the Zeromotor, a perpetual motion machine of the second kind.
Devising these machines is a favourite pastime of many eccentrics, who often come up with elaborate machines in the style of Rube Goldberg or Heath Robinson. These designs may appear to work on paper at first glance. Usually, though, various flaws or obfuscated external power sources have been incorporated into the machine. Such activity has made them useless in the practice of "invention".
[edit] Patents
Devising such inoperable machines has become common enough that the United States Patent and Trademark Office (USPTO) has made an official policy of refusing to grant patents for perpetual motion machines without a working model. One reason for this concern, according to various skeptics, is that a few "inventors" have used official patents to convince gullible potential investors that their machine is "approved" by the Patent Office.[citation needed] The USPTO Manual of Patent Examining Practice states:
- With the exception of cases involving perpetual motion, a model is not ordinarily required by the Office to demonstrate the operability of a device. If operability of a device is questioned, the applicant must establish it to the satisfaction of the examiner, but he or she may choose his or her own way of so doing. [2]
And, further, that:
- A rejection [of a patent application] on the ground of lack of utility includes the more specific grounds of inoperativeness, involving perpetual motion. A rejection under 35 U.S.C. 101 for lack of utility should not be based on grounds that the invention is frivolous, fraudulent or against public policy. [3]
The USPTO has granted a few patents for motors that are claimed to run without net energy input. These patents were issued because, skeptics claim, it was not obvious from the patent that a perpetual motion machine was being claimed.[citation needed] Some of these are:
- Johnson, Howard R., U.S. Patent 4151431 "Permanent magnet motor", April 24, 1979
- Baker, Daniel, U.S. Patent 4074153 "Magnetic propulsion device", February 14, 1978
- Hartman; Emil T., U.S. Patent 4215330 "Permanent magnet propulsion system", December 20, 1977 (this device is related to the Simple Magnetic Overunity Toy (SMOT)),
- Flynn; Charles J., U.S. Patent 6246561 "Methods for controlling the path of magnetic flux from a permanent magnet and devices incorporating the same", July 31, 1998
- Patrick, et al., U.S. Patent 6362718 "Motionless electromagnetic generator" , March 26, 2002
- Green, Willie A., U.S. Patent 6526925 "Piston Driven Rotary Engine", March 4, 2003 "Fluid driven device utilizing a leveraged system with minimal displacement"
- Goldenblum, Halm, U.S. Patent 6962052 "Energy generation mechanism, device and system", November 8, 2005 "A chamber with a partition which lets gas molecules flow one way and not the other. The pressure which builds up on one side of the partition is used to drive a generator."
- Flynn, Joe, U.S. Patent 6246561 "Methods for controlling the path of magnetic flux from a permanent magnet and devices incorporating the same", June 12, 2001
Other patents offices around the world have similar practices, such as the United Kingdom Patent Office. Section 4.05 of the UKPO Manual of Patent Practice states:
- Processes or articles alleged to operate in a manner which is clearly contrary to well-established physical laws, such as perpetual motion machines, are regarded as not having industrial application.[4]
Examples of decisions by the UK Patent Office to refuse patent applications for perpetual motion machines include:
- Decision BL O/044/06, John Frederick Willmott's application no. 0502841[1]
- Decision BL O/150/06, Ezra Shimshi's application no. 0417271 [2]
[edit] Apparent "perpetual motion" machines
Even though they fully respect the laws of thermodynamics, there are a few conceptual or real devices that appear to be in "perpetual motion", while a closer analysis reveals them to actually "consume" some sort of natural resource or latent energy like the phase changes of water or other fluids, solar energy and natural, small temperature gradients. In general, extracting useful work out of similar devices is very hard or almost impossible, as those devices usually work with low-grade heat and with very low efficiency.
So, these devices can mostly be classified as low-power, low-efficiency energy converters (not free energy producers) which are able to use low grade energy sources, but which would be impractical or impossible to use at a large scale for mass energy production, as efficiency would be extremely low, as well as any power output- if any.
Some examples of real such devices include:
- The Finsrud Device A "sculpture" by the artist Reidar Finsrud in Norway moves inside a glass enclosure for days at a time.
- The drinking bird toy (the energy comes from small ambient temperature gradients and evaporation, and harnessing the small power output would likely disrupt the working cycle).
- A capillarity based water pump: in this case, energy would again come from small ambient temperature gradients and vapour pressure differences, although it would be far too easy for the pump to stop functioning.
- A Crookes radiometer, a partial vacuum glass container with a lightweight propeller moved by (light-induced) temperature gradients.
- Any device picking minimal amounts energy from the electromagnetic radiation around it. Some modern smart labels actually work based on that principle, using the same electromagnetic field used for "reading" them as their powersource.
Some examples of imaginary such devices:
- A ship or a large power plant using the temperature gradient and heat transfer between a large surface exposed to the sun (or another heat source) and a colder one (e.g., the sea or the ground). This would actually be a low-efficiency solar generator, far less efficient than conventional solar cells.
- Any other similar device using a combination of small temperature gradients, heat pipes, evaporation, phase transitions, solar energy, electromagnetic radiation etc.
In all of these cases the "free" energy would, in any case, come from "lesser" forms of energy already present in the environment in small quantities, and the net power outputs would be extremely small to build a large-scale generator. While it certainly is possible to convert some of the ambient's low-grade heat into useful work, that would not be, by definition, "perpetual motion", and the efficiencies are so low that such devices can only be used as toys or novelty items.
[edit] Perpetual motion in pop culture
In "The PTA Disbands!" episode of The Simpsons, Lisa builds a perpetual motion machine when there was no school due to a teachers' strike; after seeing the machine, her father Homer says: "This perpetual motion machine Lisa made is a joke, it just keeps going faster and faster," and afterwards yells at her saying "Lisa, get in here...in this house we obey the laws of thermodynamics!"
In the Playstation 2 video games Xenosaga I & II, and in the Playstation 1 video game Xenogears, the device, called the Zohar, is a form of a perpetual motion machine. It is briefly described as a Pseudo-Perpetual Infinite Energy Engine.
Thomas Pynchon's The Crying of Lot 49 includes the description of a suggested perpetual motion machine, along with an explanation as to why it doesn't work.
In the computer game The Sims, a complex (and very expensive) perpetual motion machine can be bought as a household decoration.
In the computer role-playing game Ultima VI: The False Prophet , a perpetual motion machine is on display in the museum in Britain.
One episode of the Nickelodeon program Invader Zim showcased a Perpetual Energy Generator (or as its creator likes to call it, PEG) that is never activated due to the impatience of a member of the crowd present at the activation ceremony.
In Disney's Recess, one episode shows Gretchen Grundler creating a perpetual motion machine for her science project. Upon her demonstration to the class, a team of government agents photograph the blackboard equations, consfiscate the model, and remove evidence of its existence.
A perpetual motion machine was featured in episode 10 of the anime series, Cowboy Bebop, Ganymede Elegy. It is repeatedly seen in Alisa's bar, La Fin.
In 2006, the DCI corps, Santa Clara Vanguard, performed a show entitled "Moto Perpetuo," based on the theme of constant movement in music and drill.
In the fighting game Tekken, character Bryan Fury has a perpetual energy generator built within him by Doctor Boskonovich which grants him unlimited power.
[edit] References
- ^ Cox's timepiece
- ^ 608.03 Models, Exhibits, Specimens [R-3 - 600 Parts, Form, and Content of Application]
- ^ 706.03(a) Rejections Under 35 U.S.C. 101 [R-3 - 700 Examination of Applications II. UTILITY]
- ^ http://www.patent.gov.uk/practice-sec-004.pdf
[edit] Other references
- Veljko Milković and Nebojša Simin\ (2001). Perpetuum mobile. Novi Sad (Serbia), Vrelo.
[edit] See also
- Orbo
- Steorn
- Motionless Electrical Generator
- Erke Energy Research and Engineering Corporation
- Free energy suppression
[edit] External links
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[edit] Historic
- Hans-Peter's Mathematick Technick Algorithmick Linguistick Omnium Gatherum
- Eric's History of Perpetual Motion and Free Energy Machines
- The Museum of Unworkable Devices
- Richard Clegg, "Perpetual Motion Page", richardclegg.org.
- A selection of Bhaskara-like devices
- The Bessler Wheel
[edit] Research
- "Does Perpetual Motion Exist?". 2003. [ed., explains Brownian Ratchet]
- Kevin Kilty's perpetual motion page
- Vlatko Vedral's Lengthy discussion of Maxwell's Demon (PDF)
