Perpetual motion

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Pseudoscience Alert
This topic is a pseudoscience, and is not accepted by the scientific community as a valid discipline.
Although it may use scientific terminology, it does not use scientific methodology.
Remember: just because it sounds right doesn't mean it's actually right.

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A perpetual motion or over-unity device is a device that, barring mechanical breakdown, is capable of running for an arbitrarily long period of time with no outside intervention or fuel. Such a device has never been built (except in the imaginations of some pseudoscientists and outright frauds), since the concept violates the laws of thermodynamics -- essentially, even in an ideal machine, it is only possible to get enough power out of it to power the machine itself and no more (100% efficiency), and in the real world there will always be some overhead to deal with things such as friction and the load of the machine itself.

Perpetual motion machines have been patented by the US Patent Office to the chagrin of physicists.^[1]^[2]

Perpetual motion machines fall into two categories - first order and second order.

First Order machines break the First Law of Thermodynamics, and the Laws of the Conservation of Energy - they generate more useful energy than is put into them (their efficiency >100%).

Second Order machines break the Second Law of Thermodynamics - they break even on their energy in/out efficiency (their efficiency =100%).

[edit] How to spot a perpetual motion fraud

Any claim of perpetual motion is fraudulent on its face. However, many attempt to rationalize it with ad hoc explanations -- for example, Joe Newman claims that his energy machine actually consumes the components of its motors. It is therefore necessary to insist on seeing the actual specifications and design of the device in question. Chances are, if the inventor won't share, the idea is wrong and may be a complete put-on. (Keep in mind that with a properly balanced device, it's possible to simulate perpetual motion for as long as you need to keep the audience focused. Of course, such devices are always con jobs, since they obviously are not perpetual devices internally, just very, very fuel efficient, and probably not capable of all that much real work.)