A Perpetual Motion Machine (also Perpetuum Mobile, Latin for "forever moving") is an old dream of mankind: A machine that creates more energy than it receives from the outside. (A weaker version just keeps moving on and on, without creating new energy you could put in use.) "Free Energy Device" is another name for it.
Obviously, a Perpetual Motion Machine contradicts the First Law of Thermodynamics, which states, roughly, "You can't get something from nothing." Of course, this didn't stop some people from believing in a PMM — they just insist that obviously, the First Law has to be wrong.
No Conservation of Energy applied to machines.
A perpetual motion machine of the second kind is a machine violating the second law of thermodynamics — that isolated system evolves toward maximum entropy. This involves transferring heat from colder to hotter objects without spending additional energy.note
- A Toyota commercial demonstrates a car with regenerative braking, which attempts to recapture a portion of the energy lost as the car brakes. The actor in the commercial imagines applying this same technology to a roller coaster to create a "self-sustaining amusement park." Unfortunately, he is talking about creating a perpetual motion machine. No matter how perfect the machine, heat, friction, gravity, and air resistance guarantee that this is impossible. The flaw in his idea comes from the fact that the energy expended to cause the roller coaster to start will always be greater than the energy regained from the brakes, in much the same way that hybrid cars need gas.
- The Wave Motion Engine in Space Battleship Yamato and its remake Space Battleship Yamato 2199. It functions via extracting vacuum energy from space and converting it into tachyons from which energy can be extracted. It is basically a zero point energy reactor.
- The events of Puella Magi Madoka Magica was based on the attempted creation of such machines. The incubator are extremely advanced aliens. They want to stop the heat death of the universe, which requires an energy source that can violate the second law of thermodynamics. They figure out how to turn human emotions of pain and misery into an energy source, by turning human girls into magical girls, who then turn into witches, which are in turn hunted by magical girls for the energy collection.
- The animated Harlock: Space Pirate has the Dark Matter Engine for the main ship. An alien technology that gifts the ship the ability to never refuel, rearm or repair.
- In The Absent-Minded Professor and its remake Flubber, Flubber is a perpetual motion substance.
- In Battlefield Earth, the planet Psychlo has an atmosphere that spontaneously ignites in the presence of radiation. This means radioactive decay does not naturally occur on the planet, meaning the planet ignores the second law of thermodynamics and is effectively a perpetual motion machine.
- In the book, Psychlo's atmosphere has the same implausible property. But, there, it's stated that the Psychlos are actually from a different universe with different physical laws.
- The action-comedy Knight and Day revolves around three forces of people trying to secure a prototype Perpetual Energy battery.
- The train in Snowpiercer never stops, never needs refueling, and the engine does not appear to be a nuclear reactor. But while the engine is perpetual, its parts aren't, necessitating some creative replacements over time.
- In the second Jim Button book by Michael Ende, the protagonists invent it. Essentially, their version is based on a magnet which you can switch on and off, which pulls their locomotive.
- Violating the Law of Conservation of Momentum as well.
- Discussed in Komarr. One of the physicists Miles calls in to consult determines that the device he's asking her about looks like a perpetual motion machine. Since she's a competent physicist who doesn't believe in such things, she concludes that it must be drawing energy from the deep structure of the wormholes it gets pointed at — because there's nowhere else it could be coming from.
- In Atlas Shrugged, John Galt's engine relies on perpetual motion.
- The main focus of the first episode of The Chronicles of Professor Jack Baling is what happens to an engineering professor when he encounters a working perpetual motion machine. Specifically, an overbalanced wheel.
- An 8th grade student in Yevgeni Veltistov's The New Adventures of Elektronic claims to have created a small device that causes a little light bulb to light up and never go off after you wind the crank once. When the titular android character is asked if such a thing is possible, he simply says that he doesn't know, but that the device doesn't have any moving parts (except, obviously, the crank). The device is put on a shelf in the classroom and forgotten. It's mentioned that it worked without anyone touching it for weeks, but the little light bulb burned out shortly after. Of course, this is the same book where another student from the same class proved Fermat's Last Theorem, only to rip up his proof a week later, as he did not want recognition.
- Isaac Asimov's short story "The Billiard Ball" (reprinted in Asimov's Mysteries) is about a zero-gravity device which, when the zero-g field is established, the field becomes a brightly-glowing cylinder of hard vacuum — because any air molecules in it lose all proper mass, and thus become incapable of movement at other than the speed of light, so they smash their way out of the field. It's explained by the main scientist character that they get the energy to do this (from nowhere) because in abolishing gravity, the field repeals the law of conservation of energy.
- In Robert Reed's An Exaltation of Larks, time travelers from the heat death of the universe have been steadily making their way back to the Big Bang (at 15 month intervals) in order to tweak the laws of physics to make the entire universe a perpetual motion machine - rather than slowly succumbing to entropy, the universe will periodically collapse and then expand again.
- Leo Tolstoy tells a folk story about a Russian peasant who tried to invent this but failed. The man was quite capable of building mills and claimed to even have repaired mills where professional engineers failed, but lacked education, and so wouldn't know about the laws of thermodynamics.
- Discworld: Alluded to at the end of The Fifth Elephant. One of the valuable artifacts recovered is a pair of 1cm cubes that rotate in opposite directions about once a minute, no matter what. It's explained that ancient dwarven civilizations used this minimalist PMM in conjunction with a massive gear and pulley system to power absolutely everything.
- The Dream of Perpetual Motion. When Prospero Taligent diverts his company's resources to building a perpetual motion machine, his stock plummets as it's regarded as a sign he's become a literal Mad Scientist. Ten years later he claims to have succeeded, installing his only model in a Cool Airship designed never to land. The protagonist realises however that the airship is slowly losing power and will eventually crash.
- The titular Eternal Flame from the Greg Egan novel is a hypothetical chemical reaction that never exhausts itself, or at least one that continues for an absurdly long period of time, AND can be controlled and put to practical use, such as powering the Generation Ship. They spend an entire book trying to harness the explosive properties of orthogonal matter as fuel, only to develop an utterly unrelated type of engine that is just insanely efficient and runs on light. All of the (near-)perpetual motion, without the risk of catastrophic explosion.
- In the Girl Genius novel Agatha H. and the Clockwork Princess, it's mentioned in passing that one of the minor Sparks with the circus exhibited a perpetual motion machine, and was utterly mortified when Agatha proved that it needed a small push every ten years to keep going.
- In the Thursday Next series, Thursday's uncle Mycroft invents the "Nextahedron", a solid shape that is perpetually unbalanced. When unrestricted on a flat surface, the Nextahedron never stops wobbling, falling over onto a different face, wobbling again, and so on.
- In The Mouse and His Child, the eponymous characters seek to become self-winding, effectively making themselves this. Eventually, someone comes up with the clever idea of connecting two wind-up motors together so that they wind each other. Despite this being a book about sentient wind-up toys and talking animals, however, this ends up being treated realistically, as the motor still winds down over time - but it undeniably lasts much longer than it used to.
- One of the plot hinges of Angels & Demons is that the production of antimatter has not only been vastly improved in efficiency, so that large amounts can be made (and stored), but it can now be made at a cost of less energy than will be yielded by annihilating it.
- The Ransom Apparatus of The Rise of Ransom City, a machine that utilizes the Ransom Processnote to "[strip] away the world and [reveal] the energy that lies beneath," generating both light and heat in infinite quantities (among other things, like altering local gravity and creating "ghosts" of people from alternate universes). It only works because it incorporates a rune of the First Folk in its construction. Folk magic not being a toy, the Process can be very dangerous when it melts down. While Ransom intended to use it to provide free light to everyone in the West, everyone else is more interested in its applications as a Phlebotinum Bomb.
- The orrery in the Edgewood house in Little, Big: or, The Fairies' Parliament is apparently a perpetual motion machine powerful enough to supply all the energy needs of the house when no electricity is available. It may or may not technically qualify as one since it's driven by the actual motion of the planets via sympathetic magic, so it breaks the laws of nature but not actually the laws of thermodynamics.
- Barney Miller: In "The Inventor", the inventor, Mr. Emery, claims that he has invented a battery that will never run out of energy, and that his bosses at Powerite Electronics suppressed his invention because they realized no one would buy batteries anymore. When Mr. Essex from Powerite shows up, he dismisses Mr. Emery as a nutcase—but he is determined to confiscate Mr. Emery's blueprints.
- Red Green attempted to make one in the "Handyman's Corner" segment of the Grand Finale of The Red Green Show, using only household items. He hooks up a lawnmower to an alternator that powers a ceiling fan located amongst some corn stalks. The fan chops off an ear of corn when the corn gets as high as an elephant's eye, sending the corn into a sink with garbage disposal also powered by the alternator. The corn then falls into an oil drum where it decomposes into ethanol, where it gets siphoned back into the lawnmower. Meanwhile, the spare corn seeds gathered by the garbage disposal slide down a downspout to where the corn grows, so the corn keeps on coming. However, Red finds one problem in his "ultimate project". The lawnmower won't start. (And, of course, even if it had worked, it wouldnt have been a true free-energy machine, because it depends on the input of external energysunlightto grow the corn.)
- Mythbusters tested a bunch of free energy devices. All but one of them completely failed. The one that produced any energy was a contraption where liquid in a bunch of tubes connected to a wheel would be heated by the sun, boiling the liquid, causing a shift in the mass of the object, and making the wheel spin. However, it only produced a tiny amount of power, and it wasn't a true perpetual motion machine as it got its power from the sun. Effectively it was an overly complicated and inefficient solar panel.
- Snowpiecer in the television adaptation is played more realistically than the semi-mystical film version, but it is nevertheless an engine that not only perpetually generates energy, to the point of being able to get the entire train moving from a dead stop, but actually generates more energy when the train is in motion, providing power and heat to the other cars. All without any apparent source of fuel.
- The titular structure in The Eternal Cylinder, a massive, seemingly-endless rolling-pin-like device that crushes everything in its path. It's not clear exactly what powers it, and on occasion begins glowing red and starts rolling faster. While special towers, when activated, can halt it in its tracks, it can only be delayed temporarily, but never truly stopped.
- In Crusader Kings II, if you're lucky enough to defy RNG and successfully complete the immortality event chain, there's a chance another immortal can appear down the line and try to kill you. With a high enough Stewardship skill, you can have your guards trap him in a giant hamster wheel for eternity, giving your capital +20% tax income and -25% build cost & time modifiers.
- In Dwarf Fortress the mechanical energy needed to pump water up one story is only one-tenth the amount generated when the water comes back down and powers a water wheel. Power the pump with the water wheel, prime it once with manual labor, and it will endlessly generate power.
- Portal fans have proposed several ideas for perpetual motion machines using the portal technology. Most of them revolve around the fact that if one portal is on the ceiling and the other is on the floor, any object thrown in would fall indefinitely.
- Poké Balls are able to change in size from a ping-pong ball to a baseball, convert Pokémon and items into energy and store them for indefinite periods of time, simulate a "Pokémon-friendly" environment that is "designed for comfort", communicate with a Trainer's Pokédex to automatically log data on captured species, and even teleport all without a visible power source. They never need to be charged and have been shown in the anime to function perfectly after centuries of neglect. Yet this revolutionary level of technology is never shown to be applied to other aspects of life, as humanity relies on conventional forms of energy despite quite literally having perpetual energy in the palm of their hands.
- The Reapers in Mass Effect somehow work without fuel. In Mass Effect 3 Codex it is outright stated how strange and impossible this should be, as well as the fact that without need for resources and capable of replenishing their foot-soldiers from enemy ranks, the Reapers need absolutely no supply lines in war.
- The Incredible Machine has absolutely no concept of thermodynamics, making it easy to make perpetual motion machines in dozens of different forms. A power generator produces electricity from rotation, while an electric engine produces rotation from electricity. Place a generator, plug an engine into it, connect the wheels of the generator and the engine, add an initial source of energy (e.g. bellows and a windmill) - voilà! Perpetual motion.
- Try connecting a laser to a matching laser-powered outlet, and direct the beam so that it feeds itself. Now all you need is an outside laser to get the ball rolling.
- Probably the easiest perpetual motion machine you can construct is a Newton Motor with something like a tennis ball permanently set on top of it. The mouse inside the motor will continue running indefinitely so long as something is colliding with its box. Hook it up to a generator and you've got free electricity, too.
- The Trails Series has a downplayed example in the form of Septium Quartz. As soon as a machine, called an Orbment, is outfitted with the necessary amount of Quartz, it will never run out of energy and will just keep going, and it's even outright stated to be leagues better and more efficient than conventional energy sources as fuel engines were in a testing phase untill Orbal Energy was discovered. However, machinery involving Quartz can still deteriorate, malfunction and break down, meaning that the "perpetual" part mostly means it has no need to be refueled or recharged.
- There is one in the museum in Ultima VI. It's a set of gears connected by shafts; each gear transmits motion to the next, and the last one transmits it back to the first one. It has no relevance in the story, though.
- The Star Forge from Knights of the Old Republic is essentially this in both function and capability. By endlessly harvesting the practically infinite energy of a star, the Star Forge is able to create limitless amounts of droids, fighters and capital ships for those who control it. It, and everything made with the Star Forge's technology such as the Star Maps that lead to its location, are also capable of completely self-repairing themselves unless completely obliterated. Justified as it's a mechanical Eldritch Starship that is fueled by the Dark Side of the Force itself and heavily implied to be sentient.
- Xenoblade Chronicles X: The Ma-non's starship is stated to have a couple of perpetual motion machines aboard, generating power in each of its two wings. They regard these as mundane technology, one character compares how they view it to how humans view campfires. It is stated that the machine doesn't really output very much power at once though, so the Ma-non do require alternative fuels for more energy-intensive tasks.
- RWBY: In a world where real magic is thought to be a myth and Dust is becoming increasingly rare, the Relic of Creation stands out. It is a divine artifact that has the ability to keep the entire city of Atlas floating for no cost whatsoever. It is specifically mentioned that this mimics the powers of Gravity Dust; in fact, the cover story is that Atlas uses Gravity Dust instead. The only downside is that the Relic can only be used for one purpose at a time; when they come up with a plan that involves floating a different large object high into the atmosphere, they actually do have to use Gravity dust. Because of this limitation, the full powers of the Relic remain unknown.
- In Ilivais X, the titular mech is powered by one of these. How it works isn't explained, all we know is that it's so expensive that the Aztecs will throw as much military force as possible at recapturing it instead of just making another one, and that the limitless energy is the only reason the protagonist was capable of escaping in the first place. It's hinted that it may not be the energy they want, but rather something to do with the sheer fact that it shouldn't be possible, as with one rule of possibility broken, all the others can be as well.
- There's a whole gallery of plans for these machines — Donald Simanek's Museum of Unworkable Devices. Some visitors to this site misinterpret Simanek's motivation as "seeking to eliminate the flaws of such machines so that they can be made workable"; of course, his actual motivation is to educate the public that those flaws are inherent and can never be eliminated.
- The ectoentropic SCPs of the SCP Foundation all technically count as Perpetual Motion Machines, though the ones that merely create matter from out of nothing don't really fit under this trope.note
- SCP-2966 is a subversion of this trope. It is a toilet paper roll capable of producing infinite amounts of toilet paper. However, unlike many SCP objects, it follows the laws of thermodynamics. To produce the toilet paper, it draws energy from its surrounding area for an energy to mass conversion per E=MC^2. To power produce even 10 sheets of toilet paper a day, the object has to be powered by an entire nuclear power plant providing 2.04×10^17 joules of heat energy solely to SCP 2966. If the reactor fails or too much toilet paper is taken from the device per day, it will instead draw in the heat energy from its surroundings, causing the temperature of a large area to drop to near absolute zero. Inversely, if no toilet is taken, then the object will start converting mass back into energy, causing a huge nuclear explosion. The creator of the device misplaced the square in E=mc^2, meaning he wildly underestimated just how much energy is needed to create a single sheet of toilet paper.
- SCP-3238, energy drinks that either make the user burst into flames, become highly radioactive, or turn into a projectile that will quickly leave Earth's orbit, comes with the description "energy from all natural yes obeys laws of thermodynamics."
- SCP 2700 is a deconstruction of perpetual motion machines. The device as a whole is a direct energy weapon made by Nickola Tesla. However, at the center is a device that somehow reverses the flow of entropy, causing energy from going from disorganized to an organized state. Instead of being seen as an infinite power source, the SCP Foundation points out that if the object's effects spreads out of the object, it will reverse all entropy in the universe, which would kill all life forms and make a universe that would be entirely uninhabitable.
- LoadingReadyRun implies that one of these is among Paul's many dangerous, incredible, and forgotten or misapplied inventions, with James mentioning it in a list of useless things they keep around the office.
James: That machine Paul made that keeps running faster and faster?
Graham: Don't jostle that!
- Discussed in Tom Scott's "Wheels, Bombs, and Perpetual Motion Machines". Tom not only brings a machine in the Royal Institution's archives to demonstrates the flaws of one possible design, but also discusses in clear terms why it wouldn't work. Dispensing with the physics and thermodynamics explanations, Tom states that such a machine would be able to power progressively larger machines until the energy output could affect Earth's rotation, and such a machine connected to itself would effectively become a bomb.
- The Simpsons, "The PTA Disbands": Lisa is going crazy while the teachers are on strike and creates a perpetual motion machine. Homer calls a machine a joke, because it keeps going faster and faster, and tells Lisa that no physics law should be broken in his home.
Homer: Lisa, get in here! In this house, we obey the laws of thermodynamics!
- In one episode of Chip 'n Dale: Rescue Rangers, Gadget claims she once found a perpetual motion machine in the garbage can after a school science fair; of course, by then, it had stopped moving.
- In an episode of ChalkZone, Protagonist Rudy Tabootie creates one of these for the school science fair using his magic chalk. This wasn't intentional, as he was just in a rush to cheat and succeed, however, the government immediately confiscates it upon its discovery in order to figure out how it works. Rudy's solution? Draw a power cord on it, making it so that it's no longer a perpetual motion machine.
- In one episode of Recess, Gretchen invented one for a school project. It was immediately confiscated by the government. The substitute teacher at the time gave her a passing grade.
- Subverted in the Gadget Boy's Adventures in History episode "These are a Few of my Favorite Flying Things". The villain Spydra succeeds in stealing Leonardo da Vinci's perpetual motion machine prototype. Leonardo takes the theft well because his machine was supposed to prove that perpetual motion is impossible. Cue Spydra yet again suffering a humiliating defeat when her flying machine crashes.
- On the Gravity Falls episode "A Tale of Two Stans", Grunkle Stan's brother and author of the journals made a perpetual motion machine for the science fair, which would have guaranteed him a college grant. Stan accidentally breaks it, which leads to his brother being denied the grant, causing a rift between the two.
- The Rocket Power episode "Great Sandcastle Race" has Oliver's team building one for the eponymous contest.
- According to classical laws of physics, in the frictionless vacuum of outer space, it is possible to have an object that will move forever through inertia, as in planetary orbits (which do slow down, but by a negligible amount). Technically, due to conservation of Angular momentum, if you spun a planet in empty space and no force or friction acts against it at all, it would spin forever. This is sometimes referred to a perpetual-motion machine of the 'third kind' (see below). However, this is just perpetual storage of an initial amount of energy. If you hook a generator onto your frictionlessly moving object to achieve the production of energy that's the whole idea of perpetual-motion machines, all it'll do is tap that initial amount of energy. The object will then slow down, and eventually stop.
- Some people claim that Zero Point Energy can be used to generate power out of nothing.
- People attempt to patent Perpetual Motion Machines. Most nations' patent offices can and will reject any at face value, but a few get patented if they are labelled as something else. Cracked has more on the subject.
- Joe Newman managed to get all the way before a Senate hearing and had thousands of fans backing him against those smarter-than-thou scientists. It ended very quickly when Senator John Glenn (who, as a former astronaut, knows a thing or two about physics) proposed that, if the machine did indeed have a higher output than input, they simply measure the output and input to see what happened.
- To this end, patent offices have made a practice of classifying perpetual motion machines according to the laws of physics they break:
- Perpetual motion machines of the first kind break the First Law of Thermodynamicsnote . Most classic forms of perpetual motion machine break this law.
- Perpetual motion machines of the second kind manage to avoid breaking the First Law of Thermodynamics, but do break the Second Lawnote . Zero-point energy machines generally fall into this, as they do not claim to create energy from literal nothing, but to exploit energy already in the system...though in doing so, they attempt to run entropy backwards.
- Perpetual motion machines of the third kind manage to avoid falling afoul of the Laws of Thermodynamics by not attempting to extract extra energy from a system, but rather manintaining a system's state indefinitely... and according to classical laws, should run forever if left to themselves (such as a planet orbiting a star). Generally, however, some other law of physics (often quantum mechanics) will demand that energy be slowly lost from the system over time.
- There have been a few cases of seemingly successful perpetual motion machines, though careful examination has always shown either a lack of credible documentation, or an external power source. In fairness to the creators, some of these cases used energy sources not well understood at the time. One in particular, Orffyreus' Wheel, is still the subject of controversy as to its functioning; however, it is believed to be a deliberate fraud.
- Dan Brown sincerely claims that his scheme for using antimatter to create endless free energy (a major plot device in Angels & Demons) is realistic and will someday work, despite numerous corrections from experts. (Some have pointed out that the only reason we can burn wood or coal for fuel is that the enormous energy cost of growing those trees was paid by the Sun.)
- Subatomic particles such as electrons could be considered legitimate examples of objects in perpetual motion, although whether what they do really qualifies as "motion" and not a state of being in multiple places at once (but more so in some than in others) constitutes a whole branch of physics.
- There are in fact certain exceptions to the second law of thermodynamics, mostly based upon the fact that's it not really an absolute physical law so much as a side effect of the random behavior of a very large number of particles. As you might expect, this means that on very small spatial scales (where the number of particles is less, as with nanotechnology) or very large time scales (where really unlikely things will eventually happen, as in the lifetime of the universe), violations can and will occur.