Perpetual motion

Robert Fludd's 1618 "water screw" perpetual motion machine from a 1660 woodcut. Many people think this device is the first recorded attempt to describe such a device in order to produce useful work - driving millstones.

Perpetual motion refers to a movement that goes on forever once started without additional energy added. A machine that could be set in motion once would continue to move forever. Such a device or system would be against the law of conservation of energy. This law states that energy cannot be created, or destroyed, but one form of energy can be transformed into a different one.

Perpetual motion machines have interested inventors for a long time, and even though it has been shown that such a machine cannot exist, people still try to build them.

Perpetual motion machines have been classified into different types. Each type breaks a different law of thermodynamics:

1. A perpetual motion machine of the first kind produces energy from nothing. It gives its user unlimited free energy. It violates the law of the conservation of energy.
2. A perpetual motion machine of the second kind spontaneously converts thermal energy into mechanical work. In itself, this does not violate the law of the conservation of energy, because there is the same amount of mechanical work than there was of thermal energy. Such machines violate the Second law of thermodynamics. Real heat engines, such as those found in cars, also convert heat energy to work. Such engines have two reservoirs: the heat is transferred from the hot one to the cold one. Some of the heat is converted into mechanical work, the rest is used to heat the cold reservoir. Perpetual motion machines only have one reservoir for the heat. For this reason, they can convert all the heat into mechanical work.
3. A perpetual motion machine of the third kind is one that can eliminate effects like friction and other effects that use energy. Because of the inertia of the mass, it can therefore maintain motion forever. This violates the third law of thermodynamics. Although it is impossible to make such a machine, because the loss of energy cannot be completely eliminated in a mechanical system, it is still possible to reduce the loss a great deal. Even if such a machine could be built, it could only be used to store energy forever, and not to produce energy. A frictionless flywheel, for example, would eventually slow down and stop if its kinetic energy were tapped for useful work, and we would get no more energy out than the amount that was initially put in to spin up the flywheel.

Perpetual Motion Media

• Something for Nothing (1940), a short film featuring Rube Goldberg illustrating the U.S. Patent Office's policy regarding perpetual motion machines (and the power efficiency of gasoline)

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  The device shown is a "mass leverage" device, where the spherical weights on the right have more leverage than those on the left, supposedly creating a perpetual rotation.

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  Perpetuum Mobile of Villard de Honnecourt (about 1230).

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  The "Overbalanced Wheel", annotated with distances of the weights from the centreline showing that the torques on both sides even out on average

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  Perpetual motion wheels from a drawing by Leonardo da Vinci

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  Boyle'sSelfFlowingFlask

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  Ellipsoid paradox surface and rays emitted by body A in the direction of body B. (a) When bodies A and B are point like, all rays from A must be incident on B. (b) When bodies A and B are extended, some rays from A will not be incident on B and may eventually return to A.

Notes

• Veljko Milković and Nebojša Simin (2001). Perpetuum mobile. Novi Sad (Serbia), Vrelo.
• Schadewald, Robert J. (2008), Worlds of Their Own - a brief history of misguided ideas: Creationism, flat-Earthism, energy scams, and the Velikovsky affair, Xlibris, ISBN 9781462810031

Other websites

• Perpetuum Mobile Video.
• [1] Archived 2009-04-25 at the Wayback Machine Perpetual park video.
• Perpetuum Mobile Archived 2007-05-19 at the Wayback Machine Site.