Perpetual motion machine

A perpetual motion machine, also known as a perpetuum mobile (Latin), refers to a hypothetical machine that keeps operating forever or produces more energy than it consumes. It is considered impossible by the laws of thermodynamics.

Thermodynamics
In thermodynamics one distinguishes between two sorts of perpetual motion machines:

In summary, a perpetual motion machine of the first kind, which produces more energy than it consumes, breaks the first law of thermodynamics,  the law of conservation of energy: "Energy cannot be created nor consumed, only transformed". A perpetual motion machine of the second kind breaks the second law of thermodynamics, which in its common version says "Work is needed to transport heat up a temperature slope".
 * 1) A perpetual motion machine of the first kind can hypothetically create energy out of nothing, or what amounts to the same thing, it supposedly can increase a given amount of energy without any energy input. A perpetual motion machine of the first kind contradicts the first law of thermodynamics. The first law states that the amount of energy in the universe is constant, that is, if the energy content of a physical system seems to increase, this energy must have been transferred from somewhere else, it cannot have been created out of nothing.
 * 2) A perpetual motion machine of the second kind is a machine that extracts heat from a body, such as the sea or the earth and converts it into work (i.e., into useful mechanical or electric energy). Subsequently, the work generates heat that is given back to the body in the same amount as was originally extracted from it. This cycle does not violate the first law, but is in contradiction to the second law of thermodynamics. This law states that it is impossible to extract heat from a single body, and thereby cooling the body, without doing work. An air conditioner and a refrigerator need work (usually done by an electric motor) to transport heat from a cold to a warm place.

Usage in frauds
It is not uncommon for people to claim to have a perpetual motion machine from which one could generate mechanical or electric energy. These people are usually very secretive about their work and need sponsors while claiming that the secrecy is to protect them from certain entities that might oppose systems that provide free energy.

Claims of feasible perpetual motion machines exist even now in the 21st century. In particular, the Yubileiny (Jubilee) satellite launched by Russia in May 2008 was reported to use a perpetual motion machine for its propulsion,  called gravitsapa. Russian publications indicate that huge funds are used for this and similar projects.

As of March 2010, there has been no official statement from the Russian government regarding the reported use of a perpetual motion machine in the Yubileiny satellite. In 2010, the claim for the perpetual motion was denounced, but the claim for the support-less propulsion by the gravitsapa was not withdrawn (at least not before early 2010). If such propulsion were to exist, it would enable the measurement of the inertioid's absolute speed (a speed independent of frame of reference). One just has to divide the power that the inertioid takes for its propulsion by the force it provides.

A frame-independent speed of a body with non-zero rest mass violates Lorentz and Galilei invariance of, respectively, relativistic and non-relativistic mechanics. While the experimental evidence of measurement of the absolute speed by any inertioid is not reported, all the inertioids should be treated as the perpetual motion machines.

In 2006, an Irish company called Steorn claimed to have invented a magnetic 'free energy' machine dubbed the 'Orbo' - these claims were propagated on a number of technology blogs and news outlets more traditionally associated with discussing Web 2.0 services. Despite numerous statements by scientists - including statements by a 'jury' of scientists selected by Steorn - that the claims made for the machine were scientifically implausible, Steorn continues to promote and license their claimed invention.

Patent system
Since patent systems were put into use, they have received a number of patent requests for perpetual motion machines. The U.S. Patent Office now requires a working prototype in order to grant a patent for a perpetual motion machine.