Perpetual Motion and "Free Energy" machines
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Perpetual Motion and "Free Energy" machines are machines that give out more energy than is put into them (although technically Perpetual Motion machines merely require zero loss of energy). Free energy machines break the laws of thermodynamics (normally the first although some of the claimed mechanisms break the second and third as well). Sometimes, an attempt is made to work around the first law by invoking Zero-point energy.
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[edit] History
Many, many Perpetual Motion machines have been designed and not a few built. All of them failed, although a few appeared to work due to using outside sources of energy by ingenious means.
[edit] Refuting Perpetual Motion
Perpetual Motion machines, as a concept, are useful in the study of some of the subtleties of physical laws. Often they may be presented as exercises, in which a student must identify the flawed analysis of such a device.
The failure of an actual working model may be plausibly attributed to lack of funding and engineering difficulties. This, unfortunately, often makes it necessary to discuss perpetual motion and free energy from an abstract theoretical standpoint, since working demonstrations continue to be nonexistent.
A free energy device is claimed to violate the laws of thermodynamics. Thus, from a purely argumentative point of view, refuting a claim of free energy merely by citing the laws of thermodynamics would be begging the question. Since the first law can be derived from more basic laws of Newtonian mechanics, it is sometimes possible to refute a claim of free energy from simpler assumptions. If even the laws of mechanics are questioned, then we may stop and insist on a demonstration.
[edit] Present day
Most modern purported free energy machines are based around electricity or magnetism. A significant number are used as part of a scam to get people to invest money in the phoney invention.
[edit] Free Energy Devices "of the first type"
A first type free-energy device is one which produces more work than the energy supplied to it. That is, it violates the First Law of Thermodynamics, and "creates energy". The term "over-unity" is sometimes used, referring to an efficiency of greater than one.
It is common to refute such devices by invoking the impossibility of a frictionless surface. However, the first law of thermodynamics does not rely on such a restriction. Even granting the possibility of a frictionless surface, these devices are understood to be impossible according to the laws of physics. Thus it is specious and misleading to use a "friction" argument in refutation of a "first type" of free-energy device.
[edit] Overbalanced Wheels
The earliest forms of perpetual motion machines probably evolved from waterwheels, in which a net torque is maintained on a wheel, causing it to spin and do work.
One example is a simple spoked wheel in which weights are attached to the spokes at different distances from the center. Weights further from the axle will exert greater torque upon the wheel. The idea then, is to have weights further from the axle on one side of the wheel, and closer to the axle on the other side. This causes the wheel to be “overbalanced”, and to rotate, doing work. As the wheel rotates, the weights are moved closer and further from the axle, perhaps by mechanical linkages, perhaps by the effects of permanent magnets arranged around the wheel.
The erroneous analysis of such devices often fails to consider the work required to move the weights along the spokes. Or, the force used to move the weights also imparts a torque to the wheel that opposes the torque of the weights.
[edit] Buoyancy-related
[edit] Electromagnetic
[edit] Free Energy Devices "of the second type"
A second type free-energy device is one which extracts heat energy by decreasing the entropy of the system. A simple hypothetical example is an electric heater "run backwards". Whereas an electric heater consumes electricity and warms air, running it backwards should cool the air and produce electricity. This does not violate the First Law of Thermodynamics, but it does violate the Second Law.
[edit] "Feynmann's Windmill"
Feynmann's Windmill consists of a set of paddles immersed in a fluid. The paddles attach to a shaft, and at the end of the shaft, outside the fluid container, there is a one-way mechanism, consisting of a cog-and-pawl ratchet. The naive expectation is that Brownian motion will joggle the paddle-wheel this way and that, and that the ratchet will restrict the motion in one of these directions, so that the windmill will go round and round.
In fact, it can be shown that this behavior only obtains when the ratchet is colder than the fluid. You can even drive the windmill "backwards" by heating up the ratchet.
Reference: The Feynmann Lectures in Physics volume 1, chapter 46.
[edit] "Maxwell's Demon"
Maxwell's demon is a little tiny guy who guards a door between two containers of an ideal gas. It is assumed that opening and closing the door requires a negligible amount of energy. Whenever he sees a fast-moving molecule of the gas coming from the left, he opens the door and lets it through. If he sees a slow-moving molecule coming from the left, he keeps the door closed. Likewise, if he sees a slow-moving molecule coming from the right, he lets it through, but blocks fast-moving molecules. Thus the temperature of the gas in the container on the right increases, and that on the left decreases.
It is possible to show that no such demon can exist, since a detector capable of determining the speeds of approaching molecules would necessarily do work upon those molecules, requiring an external energy source.
[edit] One-way mirrors
One device that apparently violates the Second Law uses two rooms separated by a "one-way mirror", of the type seen in police interrogation rooms. Thermal radiation from the gas in one room is admitted to the other, where it is absorbed by the gas there, heating it. Thermal radiation from the other room is reflected by the mirror, where it is re-absorbed in the same room. Over time, the gas on the "mirror" side should become warmer, and the gas on the "window" side should become cooler.
This device does not work, since a "one-way mirror" does not function as described here. A one-way mirror actually admits the same amount of light from either side. In the police interrogation room, the use of a much higher lighting level on one side causes the reflected image to overwhelm the transmitted image on that side.
[edit] Negative resistance
Resistance is a term for the ratio between the voltage across a conductor and the current through it. For many substances, this value is often fairly constant (a fact known as Ohm's Law). The value is always positive, reflecting the fact that current flows from a point of higher voltage to a point of lower voltage.
It is interesting to consider a hypothetical object with negative resistance. Such a substance would have an electrical current against the voltage, which could be used, for example, to recharge batteries or run electrical appliances. This would not necessarily violate the First Law of Thermodynamics, since "Joule's Law" predicts that a negative resistor would cool down rapidly as it produced energy. This would violate the Second Law of Thermodynamics by decreasing the entropy of the system.
There are objects in which the resistance drops as the voltage increases. A fluorescent light tube is one common example. This phenomenon is technically called "negative differential resistance", but the term "negative resistance" is commonly used. This misnomer has caused great excitement among free-energy inventors, who mistake it for actual negative resistance. No substance exhibiting negative resistance has ever been found.
[edit] Free Energy Devices "of the third type"
A third type of free-energy device is one which extracts energy from some inexhaustible reservoir, such as a parallel universe, a tachyon world, etc. This definition is a bit vague; at one time, "inexhaustible reservoirs" might have included subterranean oil, the Niagara River, etc.
[edit] Zero-point energy
[edit] List of purported free energy machines
- Testatika
- Joseph Newman's Electromagnetomic Motor
