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See also perpetuum mobile as a musical term
Perpetual motion machines (the latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which produce useful energy "from
nowhere." The existence of a perpetual motion machine is generally accepted as being impossible according to current known laws
of physics. In particular, perpetual motion machines would violate either the first
or second laws of thermodynamics. According to which law is violated,
perpetual motion machines are divided into two subcategories, referred to as perpetual motion of the first kind and perpetual
motion of the second kind. There is always a chance that the accepted laws
of physics are wrong, but a lot of evidence is needed to regeneralize
these.
Physicists may try to test their knowledge of physics by proving, without using thermodynamics, that a proposed perpetual motion machine
cannot work. Also, sometimes physicists will discover "apparent" perpetual motion in thought experiments. Such "paradoxes" expose
misunderstandings of the meaning of accepted physical theories and are considered quite
instructive.
Because the principles of thermodynamics are so well established, serious proposals for perpetual motion machines are met with
disbelief on the part of physicists, which makes a discussion of the merits of the proposal difficult if not impossible.
Serious discussions of perpetual motion usually occur only when dealing with the topics of open systems, aether theories, free energy, and vacuum energy.
Criteria
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 disorder (entropy) always increases; another statement is that no engine can be
more efficient than a Carnot heat engine. See the respective
articles, and thermodynamics, for more information.
Machines which claim not to violate either of the two laws of thermodynamics but rather claim 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.
Kinds of Violations
First Kind
A perpetual motion machine of the first kind produces more energy
than it uses. Therefore, once started, the machine can go on forever. This is prohibited by the Law of Conservation of Energy.
Many of these designs utilize magnets as some kind of free energy source, and assume
frictionless surfaces. However, while several of these designs are not perpetual motion machines, they often times can run on
their own for a long time, as long as they're not asked to do any real work to the external environment.
Second Kind
A perpetual motion machine of the second kind is one which converts heat completely into other forms
of energy. Such a device would violate the second law of thermodynamics (see also entropy) and would be viewed with great skepticism.
Thought experiments
As stated in the introduction, serious work in theoretical
physics often involves thought experiments that test the boundaries of understanding of physical laws. An incomplete list of
such includes:
- 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
- "Cosmic background space drive": where redshift/blueshift of the background radiation is used to drive a rocket's engine
An incomplete list of proposed experiments:
- Casimir Cones: the basis for almost perpetual motion machine fueled by entropy, which exploits the Casimir effect
Inventions and Patents
Main article: History of perpetual motion machines
The invention of perpetual motion 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, but have various flaws or obfuscated external power sources that render them useless in
practice.
This sort of "invention" 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. The
USPTO granted a few patents for motors that are claimed to run without net energy input. These patents were issued because it was
not obvious from the patent that a perpetual motion machine was being claimed. These are:
- Johnson, Howard R., US4151431 "Permanent Magnet Motor", April 24,
1979
- Baker, Daniel, US4074153 "Magnetic propulsion device", February
14, 1978
- Hartman; Emil T., US4215330 "Permanent magnet propulsion system", December 20, 1977 (this device is related to the Simple Magnetic Overunity Toy (SMOT))
Proponents of perpetual motion machines use a number of other terms to describe their inventions, including "free energy" and "over unity" machines.
See also
- Main: History of
perpetual motion machines, Open
system, Vacuum energy, Radiant energy, Free
energy, Negative resistance, Brownian ratchet
- Science: Conservation of energy, Thought experiment, Thermodynamic entropy, Second law of thermodynamics, Kirchhoff's Laws
- People : George Westinghouse, Josef Hoëné-Wronski
- Other: Perpetuum mobile, Mad scientist, List of disputed theories
External links, resources, references
Historic
Research
Patents
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