Almost Perpetual Motion

Some mechanisms come very close to the idea of perpetual motion machines or they seem to contradict the principle of energy conservation. But there is no black magic used, as everything has an often simple natural explanation.

Drinking Bird

By courtesy of Ostrach-Glas

     Many readers will know the toy which mimicks the behaviour of a drinking bird. Body, neck and head of the bird are made of a sealed glass tube, partly containing a liquid. The bird itself has two feet and can swing between these. If a glass full of water is placed in front of the toy and the head dipped into the water once, the bird continues and swings forth and back.

How does it work? The secret of the principle is the vaporisation energy . The liqiud inside the bird vaporizes easily. The head of the bird is covered with cloth or felt, which can hold some water. If the bird dips in, the liquid inside the bird runs down to the body and the bird moves up. The water at the head vaporises and by this cools the content of the tube. The liqid inside the toy condenses and the head of the bird gets heavier, so that the bird dips in again. The whole cyclic process runs as long as water is in the glass.

Perpetual Clock

In 1658, Otto von Guericke named the water or mercury barometer semper vivum, which is literally the same as Perpetuum Mobile. It is a close idea to utlize these movements of a liquid column to operate a little machine. The seventeenth century already saw the invention of some clockworks being wound up by barometric devices. Some of these machines were ridiculously large and had a weight of some hundred pounds! All this effort to keep a clockwork running. We have to keep in mind, that the aneoride barometer was invented much later.

Other clockworks were powered by concealed springs. All these clocks were designed for long running time. It is no surprise that some of them were thought to be real perpetual machines.

By courtesy of Mike Murray
     The Swiss company Jaeger-Culture manufactures a modern variant of a perpetual clock under the trademark "Atmos". This clock is wound up by changes of temperature and air pressure, which are even in well-climatized rooms rooms sufficient to keep it running.

Heat Pump

The efficiency of a modern heat pump often is given by figures of 250% or even 300%. Is this a Maxwellian demon in technical disguise? Not at all. In order to win energy, you have to get it from somewhere. In this case, the heat pump tranfers energy from one reservoir (e.g. ground water) to another reservoir (e.g. a warmwater tank in your cellar). The energy bilance is positve in commercial terms. But if we look at the whole system, a heat pump increases the entropy by using power to pump energy. The "loss" is the energy used to drive the pump and some thermal losses of the pumped thermal energy between the reservoirs.


It is a well-known fact that chemical reactions do not only work in the desired direction, but can be reversed in many cases. Until the mid-1950ies, the chemical world was dominated by knowledge about reactions which need particular conditions (e.g. temperature, pressure) for a maximum of resulting product. This always was found to be some sort of equilibrum between the desired direction and its reversed reaction. For commercial applications, chemists try very hard to find the conditions for their processes which guarantee an optimum of the desired product at manageable cost and technical effort.
In 1955 the chemists had understood how the citrate acid cycle in organisms worked. In the USSR, a certain Mr. Belousov wanted to reproduce a simplified variant of this cycle at small scale in his lab. Belousov had success and found an oscillating chemical reaction. That was in sharp contradiction to the well-established theory, and apparently violated the second law of thermodynamics. It's no surprise that Belousov had enomous problems to publish his discovery of oscillating chemical reactions. He was treated as a crackpot and fraud. His second attempt at the beginning of the 1960ies led to a tiny footnote in a scientific conference's papers collection. Belousov gave up. The establishment had won - and was wrong in his case.
In 1968, Mr. Zhabotinsky learned of Belousov's results and experimetally checked them, which is neither difficult nor expensive. And he could reproduce the experiment. Now the time had come for the acceptance of the results. Today we know more about these reactions and how entropy sinks can spring up in complex chaotic systems. The second law still is unviolate.

And what about Belousov? He received the Lenin medal for his sensational discovery. Posthumously. chapter

Last update: 22 May 2004 /
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