Whether you supply energy yourself or get it from a draught animal, steam engine, hydro-electric dam, gas turbine or any other manner, you will have to put effort into obtaining it, either directly or indirectly by the work you do to pay the bill. Furthermore, generating the energy in usable quantities is frequently a messy business, with often serious environmental effects accompanying the damming of rivers or the generation of large quantities of manure, smog, fly ash, and so on. Even the large-scale development of wind, tidal and solar power would have considerable environmental drawbacks, despite the enthusiasm of their advocates. One solution to this problem is to improve the efficiency of your generator. This will allow you to produce more energy per unit cost, whether that cost is measured in direct monetary terms, pollution , destruction of habitat or any other means.

Herein lies the attractiveness of the perpetual motion machine. If you can develop a device which generates more power than it consumes, or can make available sources of energy which are otherwise unavailable, you can run your entire economy on a AAA cell. Other than the fact that it sounds too good to be true, there is no obvious reason why this should not be possible. The physical concept of energy (let alone of its conservation) is less than two hundred years old, so clearly it doesn't qualify as "obvious". Recorded attempts to achieve perpetual motion go back at least 15 centuries. Medieval attempts to achieve this are well documented and some deserve to be regarded as examples of serious engineering design despite their inevitable lack of success. It was not until the end of the seventeenth century that Newtonian mechanics and the calculus were available to demonstrate that the more obvious proposals were unable to generate the net force or torque required for their continued operation. However, the belief in achievable perpetual motion by other means was still a reasonable stance until well into the nineteenth century, during which time our understanding of the relevant physics gradually unfolded. Here is a partial list of the more important events:

• Thomas Young introduces the physical concept of energy (1807)
  
• Sadi Carnot performs a scientific analysis of steam engine efficiency (1824)
  
• James Joule and Julius Meyer establish the mechanical equivalent of heat (1843)
  
• Hermann Helmholtz states the first law of thermodynamics (1847).
  
• Rudolf Clausius states second law of thermodynamics (1850).
  

The analysis and dismissal of electromagnetic perpetual motion machines was made possible when the new science of electromagnetism was put on a firm footing by James Maxwell (1865). (However, the previously stated laws of thermodynamics were general statements not restricted to purely mechanical devices.) So, towards the end of the last century there were sound reasons to believe that all attempts to achieve perpetual motion were futile.

Although the possibility of constructing a perpetual motion machine is dead as a topic of serious discussion, the analysis of proposed perpetual motion machines is often interesting, exposing conceptual errors and illustrating important theoretical points to students. This is mostly true with the earlier machines, for which the design details are clear and a proper physical analysis can be made. Unfortunately, many of the new breed of perpetual motion machine are so vaguely described (often assuming nonexistent physical entities) that proper analysis is impossible. Much of the reason for this lies in the frequent and inappropriate use of the terminology and concepts of relativity and quantum mechanics.

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