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A '''Perpetuum Motion''' (lat: eternal movement) device is a hypothetical machine which is said to be able to produce work indefinitely without energy sources or produces more energy than it consumes.

A '''perpetual motion''' (lat: eternal movement) device is a hypothetical machine which is said to be able to produce work indefinitely without energy sources, or produces more energy than it consumes. Until today, no functioning perpetual motion device has been known of, although numerous lay persons, individual researchers, and pseudo-scientists have tried to construct such a device.

A great number of inventors claim they have built a perpetual motion machine, but none of them succeeded in proving this. Often these claims were made by fraudsters and scammers. Since such a device, if working, violated the laws of thermodynamics, it is also scientific consensus that it is impossible. Despite this fact, the pursuit of perpetual motion devices remains popular.

A great number of inventors claim they have built a perpetual motion machine, but none of them succeeded in proving this. The field of perpetual motion research is also haunted by a fair share of impostors. These persons will often avoid the term perpetual motion and rather describe their devices as 'converters'.

==Classes of Perpetuum Motion devices==

 

==Classes of Perpetual Motion Devices==

[[image:pmleonardodavinci.jpg|PM according to Leonardo da Vinci|left|thumb]]

[[image:pmleonardodavinci.jpg|PM according to Leonardo da Vinci|left|thumb]]

[[image:BesslerRad.jpg|PM Bessler Rad|200px|thumb]]

[[image:BesslerRad.jpg|PM Bessler Wheel|200px|thumb]]

From a theoretical point of view, these machine are classified by the law they would violate:

From a theoretical point of view, these machines are classified into three categories based on which law of thermodynamics they violate:

*Perpetuum Motion device of the first kind: This machine produces energy without input, or more energy than it consumes, and therefore violates the first law of thermodynamics. This kind is also called "overunity" by its supporters.

*Perpetual motion device of the first category: This machine would show an efficiency of more than 100% (PM supporters will also call it 'overunity'). Such a device will be in violation of the first law of thermodynamics, the law of energy conservation, as it would produce energy from nothing.  

*Perpetuum Motion device of the second kind: This machine converts heat to mechanical energy. Since this cools the environment, it cannot go on forever and violates the second law of thermodynamics.

*Perpetuum Motion device of the second category: This machine will work cyclically and and will take the energy necessary from a heating bath. Such a device will be in violation of the second law of thermodynamics, since the total conversion of work into heat happens to be irreversible. Heat pumps therefore  may not be seen as a second category PM.

*Perpetuum Motion device of the third kind: A machine that runs indefinitely without doing any work. The idea is that, if friction is completely removed, such a machine might run forever. And while it is impossible to achieve, it is however possible to come pretty close. Such devices have actually useful appliances e.g in the construction of flywheels.

*Perpetuum Motion device of the third kind: A machine that runs indefinitely without doing any work. The idea is that, if friction is completely removed, such a machine might run forever. And while it is impossible to achieve, it is however possible to come pretty close. Such devices have actually useful appliances e.g in the construction of flywheels.