In the previous visual you will have noticed how it is not possible to achieve a perfect cycle when converting between two forms of energy. There is always some loss during the cycle.
Although we have only seen a very simple example, in all the ingenious devices for perpetual motion invented by man the same thing has happened. There have even been cases or notorious swindlers who invented false perpetual motion machines (one of them even managed to deceive the Czar Peter the Great, the person portrayed in the monument).

Finally the so-called second law of thermodynamics was accepted, which we could express as follows: It is not possible to achieve perpetual motion based on continuous reciprocal conversion between two forms of energy. 
As in many present-day machines, heat is used to generate movement, in the following visual we examine what form the second law presents for machines which work with energy produced by a heat source.