In order for a thermodynamic process to occur it must satisfy the 1st and 2nd laws of thermodynamic. A perpetual-motion machine is a device that violates these laws. There have been many attempts through out history to create a perpetual-motion device. However, to this date, no one has succeeded. Despite this fact inventors are still trying to create one.
Perpetual-Motion Machine of the First Kind (PMM1)
Any device that violate the first law of thermodynamics is called a perpetual-motion machine of the first kind (PMM1).
Recall that the first law is the conservation of energy law. This means that energy isn’t created or destroyed. Instead there must be an energy balance where the energy coming in and going out of the system must be accounted for.
A PMM1 typically is a device that creates energy out of nothing. This, however, is not possible since it violates the first law of thermodynamics.
Perpetual-Motion Machine of the Second Kind (PMM1)
In addition to a PMM1 there are also perpetual-motion machines of the second kind (PMM2). A PMM2 violates the second law.
The second law of thermodynamics states that energy flow is directional. For instance, heat will always flow from a source of higher temperature to a sink of lower temperature. This process cannot be reversed without additional external work energy added to the system.
A PMM2 will violate the 2nd law of thermodynamics if it reverses the natural flow of energy without adding additional external work energy to the system.
U.S. Patent Office
As mentioned above, many inventors that have tried to create a perpetual-motion machine. In fact some have even filed patents and were successful at fundraising.
For example J.W. Kelly, a carpenter from Philadelphia, got funding for an invention that could push a rail road train 3000 miles on 1 L of water. In reality this invention was not possible and as a result never happened. In fact it was discovered after his death that his prototype was powered by a hidden motor.
Since so many people were trying to file for patents for inventions that did not respect the laws of thermodynamics, after 1918 the U.S. Patent Office would no longer consider perpetual motion devices.