perpetual motion

the motion of a theoretical mechanism that, without any losses due to friction or other forms of dissipation of energy, would continue to operate indefinitely at the same rate without any external energy being applied to it.
[1585-95]

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      the action of a device that, once set in motion, would continue in motion forever, with no additional energy required to maintain it. Such devices are impossible on grounds stated by the first and second laws of thermodynamics.

      Perpetual motion, although impossible to produce, has fascinated both inventors and the general public for hundreds of years. The enormous appeal of perpetual motion resides in the promise of a virtually free and limitless source of power. The fact that perpetual-motion machines cannot work because they violate the laws of thermodynamics has not discouraged inventors and hucksters from attempting to break, circumvent, or ignore those laws.

      Basically there are three kinds of perpetual-motion devices. The first kind includes those devices that purport to deliver more energy from a falling or turning body than is required to restore those devices to their original state. The most common of these, and the oldest, is the overbalanced wheel. In a typical version, flexible arms are attached to the outer rim of a vertically mounted wheel. An inclined trough is arranged to transfer rolling weights from folded arms on one side of the wheel to fully extended arms on the other. The implicit assumption is that the weights exert more downward force at the ends of extended arms than is required to raise them on the other side, where they are kept closer to the axis of rotation by the folding of the arms. This assumption violates the first law of thermodynamics, also called the law of conservation of energy, which states that the total energy of a system is always constant. The first such device was suggested by Vilard de Honnecourt, a 13th-century French architect, and actual devices were built by Edward Somerset, 2nd marquis of Worcester (1601–67), and Jean Ernest Elie Bessler, known as Orffyreus (1680–1745). Both machines gave impressive demonstrations by virtue of their ability to operate for long periods of time, but they could not run indefinitely.

      Another unsuccessful attempt to create perpetual motion by violating the first law of thermodynamics was the closed-cycle water mill, such as one proposed by the English physician Robert Fludd in 1618. Fludd erred in thinking that the energy created by water passing over a mill wheel would exceed the energy required to get the water back up again by means of an Archimedes screw.

      Perpetual motion machines of the second kind attempt to violate the second law of thermodynamics—namely, that some energy is always lost in converting heat into work. One of the more notable failures in this category was the ammonia-filled “zeromotor” developed in the 1880s by John Gamgee in Washington, D.C.

      Perpetual motion machines of the third kind are those associated with a continuous motion that would supposedly be possible if hindrances like mechanical friction and electrical resistivity could be eliminated. In fact, such forces can be greatly reduced, but they can never be completely eliminated without expending additional energy. A prime example is the superconductive metals, whose electrical resistance disappears completely at low temperature, usually somewhere around 20 K. Unfortunately, the energy required to maintain the low temperature exceeds the work that results from the superconductive flow.

      Other types of perpetual motion machines have been proposed based on misunderstandings of the nature of certain energy sources. An example is the self-winding clock that derives energy from changes in the temperature or pressure of the atmosphere. It depends upon the energy delivered to the Earth by the Sun and is not, therefore, a perpetual motion machine.

      Scientific and governmental sanctioning bodies have looked askance at perpetual motion claims for many years. Since 1775 the French Academy of Science has refused to correspond with anyone claiming to have invented a perpetual motion machine. The British and U.S. patent offices have long refused to expend time or energy on such claims.

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Universalium. 2010.

Look at other dictionaries:

  • Perpetual motion — Motion Mo tion, n. [F., fr. L. motio, fr. movere, motum, to move. See {Move}.] 1. The act, process, or state of changing place or position; movement; the passing of a body from one place or position to another, whether voluntary or involuntary;… …   The Collaborative International Dictionary of English

  • Perpetual motion — Perpetual Per*pet u*al, a. [OE. perpetuel, F. perp[ e]tuel, fr. L. perpetualis, fr. perpetuus continuing throughout, continuous, fr. perpes, etis, lasting throughout.] Neverceasing; continuing forever or for an unlimited time; unfailing;… …   The Collaborative International Dictionary of English

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  • perpetual motion — n. the motion of a hypothetical device which, once set in motion, would operate indefinitely by creating its own energy in excess of that dissipated …   English World dictionary

  • Perpetual motion — For other uses, see Perpetual motion (disambiguation). Robert Fludd s 1618 water screw perpetual motion machine from a 1660 wood engraving. This device is widely credited as the first recorded attempt to describe such a device in order to produce …   Wikipedia

  • perpetual motion — noun motion that continues indefinitely without any external source of energy; impossible in practice because of friction • Hypernyms: ↑motion * * * perˌpetual ˈmotion 7 [perpetual motion] noun uncountable …   Useful english dictionary

  • perpetual motion — also perpetual motion N UNCOUNT The idea of perpetual motion is the idea of something continuing to move for ever without getting energy from anything else …   English dictionary

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  • perpetual motion — A situation where a device will turn forever because there is no friction between the moving part and the stationary part. Although friction can be greatly reduced, it can never be eliminated. Thus a perpetual motion machine is impossible …   Dictionary of automotive terms

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