Thermodynamics is based on three generalizations, or the principle of the first principle of thermodynamics is the law of conservation of energy; its second principle characterizes the direction of all natural, spontaneously occurring processes; a less general third principle allows one to determine the absolute value of one of the fundamental properties of matter - its entropy. These principles, or laws, which are generalizations of a huge amount of experimental material, can be expressed in different ways. They are often formulated as a statement about the impossibility of realizing Perpetuum mobile - a perpetual motion machine.
Perpetual motion machine of the first kind, in which the work performed by the machine would exceed the amount of heat supplied. A perpetual motion machine of the second kind, in which work would be carried out at the expense of one source of heat. And a perpetual motion machine of the third kind, in which work would be done by cooling the energy source to absolute zero temperature.
In 1911, Max Planck formulated the third law of thermodynamics as a condition for the entropy of all bodies to vanish as the temperature tends to absolute zero.
The third law of thermodynamics refers only to equilibrium states. It allows you to find the absolute value of entropy. In this case, the entropy of the equilibrium system at absolute zero temperature is considered to be zero.
From the third law of thermodynamics, a number of consequences can be obtained concerning the properties of substances near absolute zero.
The most important consequence of the third law of thermodynamics is the inaccessibility of absolute zero. The principle of unattainability of absolute zero was formulated by Nernst in 1912. However, Nernst's proof is inconsistent. But his assumption about the impossibility of reaching absolute zero turned out to be true.
Another important consequence of the third law of thermodynamics is the conclusion about the temperature dependence of the heat capacity of bodies at temperatures close to the temperature of absolute zero.
Perpetual motion machine of the third kind - hypothetical machines that demonstrate perpetual motion in the absence of friction (mechanisms approaching ideal - superconducting aggregates, superfluids, etc.). Perpetual motion machines of the 3rd kind, despite the name, are not engines in their pure form, rather they can be called energy accumulators.
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Perpetual motion machines of all kinds are still receiving attention from inventors. As history shows, almost every time new natural phenomena or previously unknown effects were discovered, many inventors immediately tried to use them to substantiate the possibility of perpetuum mobile and proposed new projects.