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Perpetual motions are classified by which law it breaks:

Perpetual motion of first kind breaks the first law of TD. It generates energy from nowhere.

Perpetual motion of second kind breaks the second law of TD. Examples of those include an engine or a pump with efficiency 100%.

Perpetual motion of third kind breaks the third law of TD. It conserves kinetic energy forever.

Then what about the zeroth kind? Since the zeroth law of TD defines temperature, the breakage of it will make the temperature of the motion undefined.

What kind of impossible motion could have undefined temperature?

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  • $\begingroup$ How does breaking of the third law allows perpetual motion? $\endgroup$
    – A.V.S.
    Commented Aug 12, 2019 at 8:06
  • $\begingroup$ @A.V.S. If the third law is broken, as the temperature of the motion approaches zero, the entrophy will diverge. This allows nonzero enthalpy at the situation. $\endgroup$
    – Dannyu NDos
    Commented Aug 12, 2019 at 8:19
  • $\begingroup$ QM vacuum energy generates energy from nowhere in massive quantities, and so does dark energy. $\endgroup$
    – Michael Walsby
    Commented Aug 12, 2019 at 8:55
  • $\begingroup$ @MichaelWalsby That's the first kind. $\endgroup$
    – Dannyu NDos
    Commented Aug 12, 2019 at 8:57
  • $\begingroup$ As far as I'm aware, the premise here is flawed a bit. The third law isn't directly related to perpetual motion of the third kind. Perpetual motion of the first and second kind fit nicely within the first and second laws of thermodynamics. Perpetual motion of the third kind does not fit so well with the third law of thermodynamics as far as I'm aware. $\endgroup$
    – JMac
    Commented Aug 12, 2019 at 15:17

2 Answers 2

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The zeroth low states that "The Zeroth Law of Thermodynamics states that if two bodies are each in thermal equilibrium with some third body, then they are also in equilibrium with each other." now if you can a machine which contains three parts (let's say A, B , and C) and A is in thermal equilibrium with B and B is also in the thermal equilibrium with C but A and C are not in equilibrium then you have violated the zeroth law.

Can this ever happen? no. But there is an interesting fact in probability which is similar but different. if drug A cure more people than drug B and drug B cures more people than drug C then you CANNOT conclude that A cures more people than C. You can learn more about this aspect of probability in the following video. https://www.youtube.com/watch?v=zzKGnuvX6IQ&t=3s

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Violating the zero law implies that you can create a perpetual heat transfer from the environment to some simple system (such as a gas in a container). And then you can use this increased internal energy of the system to generate work. So it is basically very similar to the second kind, you can transform random motion into macroscopical work. But it is simpler in the sense that the heat transfer happens spontaneously by simple contact between the environment and the system.

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