Famous Laws

Talking of physical laws may cause misinterpretations. The expression physical law implies that they are not going to change. But we should keep in mind that these laws are an equivalent formulation of certain properties of matter which have been observed and checked since long times. These laws are empirical. The laws only hold for macroscopic items. As we are not going to discuss quantum mechanics or the behaviour of single atoms, we can consider the laws as applicable.

The Golden Rule of Mechanics

Master-builders and craftsmen knew the so-called Golden Rule of Mechanics. Whenever you use ramps, levers or belt-pulleys, screw-winches or or mechanical equipment to lift an item, the rule says: "The less force you need, the more distance you need". The Golden Rule is an equivalent to the first law of thermodynamics.
Up to now, I haven't been able to identify the time and place where this rule originated.

The Laws' Predecessor

1775, the French Academy of Sciences published in their transactions this statement, after their scientists for long time have been bothered by many inventors of perpetual motion machines. From that time on, the Academy did not accept any reseach papers concerning perpetual motion, trisection of the angle, duplication of the cube and the circle's quadrature. The mathematical topics were regarded as postponed until a reasonably develeped mathematical theory on sound foundations had been developed.


The famous title sheet		    "La construction d'un mouvement pepétuel est absoluement impossible; quand même le frottement, la résistance du milieu ne détruiroient point à la longue l'effet de la force motrice, cette force ne peut produire qu'un effet égal à sa cause; si donc on veut que l'effet d'une force finie dure toujours, il faut que cet effet soit infiniment petit dans un tems fini. En faisant abstraction du frottement & de la résistance, un corps à qui on a une fois imprimé un mouvement le conserveroit toujours; mais c'est en n'agitsant point sur d'autres corps, & le seul mouvement perpétuel possible, dans cette hypothèse, (qui d'ailleurs ne peut avoir lieu dans la Nature) seroit absolument inutile à l'object que se proposent les Constructeurs des mouvement perpétuels. Ce genre des recherches a l'inconvénient d'être couteux, il a ruiné plus d'une famille, & souvent des Méchaniciens qui eussent pu rendre de grands services, y ont consumé leur fortune, leur temps & leur génie."
"The construction of a perpetual motion is absolutely impossible; even if the effect of the moving force is not destroyed by friction and resistance of the environment, this force cannot produce more reaction than one equal to its action.If the effect of a finite force continues, it is necessary that this effect is infinitly small after a finite time. If friction and resistance are ignored by abstraction (which in nature is not the case), an object that got a movement once, would remain in perpetual movement, but not act on other objects, and thus the perpetual motion would be completely useless in regard of the claims of their inventors. This part of research has been inconveniently expensive, it has ruined more than one family & mechanicians, who otherwise would have been of great use, have wasted their luck, their time and their genius."

We should be aware that this statement was made when the discussion around force and power, impulse and energy could be regarded as being sorted out. However, the energy principle as known today was not clearly formulated.
Today, three laws of thermodynamics are known, and one additional law that frequently is named the "zeroth law".

 The Laws of Thermodynamics

The  0th to 2nd laws are cited from Young and Friedman: University Physics, 9th ed. (Addison-Wesley 1996).

The 0th Law

If C is initially in thermal equilibrium with both A and B, then A and B are also in thermal equilibrium with each other.

The 1st Law

Any thermodynamic system in an equilibrum state posesses a state variable called the internal energy E. Between any two equilibrum states, the change in internal energy is equal to the difference of heat transfer into the system and work done by the system.

The 2nd Law

A natural process that starts in one equilibrum state and ends in another will go in the direction that causes the entropy of the system plus the entropy of the environment to increase for an irreversible process and to remain constant for a reversible process.

The 3rd Law

At absolute zero the entropy is zero.

Simple Version of "The Laws"

Some scientists may disagree, but it is easier to memorize these characteristic properties of the famous laws.

 The Perpetual Motion Machines

As already mentioned in the PMM introductory chapter, modern science distinguishes between perpetual motion machines by classifying them according to the law of thermodynacs they violate. Consequently, we should not only consider machines of the first and second kind, but also machines of the zeroth and the third kind. What types of machines are these? A general, but useless definition is:

By this definition, we do not learn how a particular machine is intended to operate and exactly why it violates a particular law of thermodynamics. Of course, a machine concept can violate more than one of the laws.

Perpetual Motion Machine of the 0th Kind

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Perpetual Motion Machine of the 1st Kind

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Perpetual Motion Machine of the 2nd Kind

A machine of this type would be able to transport heat from a cold reservoir to a warm reservoir. This sounds familiar to those who know about the Maxwellian demon. We could imagine a system in which the heat would instead be transferred from the cold object to the hot object, and such a system would not violate the first law of thermodynamics. The cold object would get colder and the hot object would get hotter but energy would be conserved.

Perpetual Motion Machine of the 3rd Kind

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Last update: 22 May 2004 /
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