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J. Perelman
"Entertaining physics". Book 1.
Chapter 4. Rotation. "Perpetual motion machines"


Eternal engine”, “perpetual motion” is often said in the literal and figurative sense of the word, but not all are aware that, in fact, it is necessary to understand by this expression. Perpetual motion is such imaginary mechanism that continuously moves itself and, in addition, performs some useful work (for example, raises the cargo). Such a mechanism none build failed, although attempts to invent it was done a long time ago. The futility of these attempts led to a firm belief in the impossibility of perpetual motion and to establish the law of conservation of energy is fundamental propositions of modern science. As for perpetual motion, then it means the continuous movement without doing the work.

The figure below shows the imaginary self-propelled mechanism is one of the oldest projects of perpetual motion, and sometimes now reviving unlucky fanatics of this idea. To the edges of the wheels attached to the folding sticks with weights on the ends. For any position of the wheel loads on the right side will be tilted further from the centre than on the left; this half, therefore, must always drag the left and thereby cause the wheel to rotate. Hence, the wheel should spin forever, at least until such time as will not fray its axis.

Imaginary forever moving wheel, invented in the middle ages

So thought inventor. Meanwhile, if you make such an engine, it will fail to rotate. Why is the calculation of the inventor is not justified?

Here's why: although the cargo on the right side is always further from the centre, but inevitably this situation, when the number of these goods is less than the left.

Look at the picture: on the right just 4 cargo, left - 8. It turns out that the whole system is balanced; it is natural that the wheel will not rotate, and, after taking a few swings will stop in this position [the Motion of such a system is described by the so-called theorem of moments].

It has now been proven indisputable that it is impossible to build a mechanism that forever would move by itself, even while performing some work. Hopelessly to work on this task. In the old days, especially in the middle ages, people unsuccessfully struggling to get their heads over her permission and spent the invention of “perpetual motion” (in Latin perpetuum mobile, pronounced “Perpetuum mobile”) a lot of time and labor. The possession of such motor seemed even more attractive than the art of making gold from cheap metals.

Pushkin in “Scenes of chivalry” put such a dreamer in the face of Berthold.

“ - What is a perpetuum mobile? "said Martyn.

- Perpetuum mobile - meets him Berthold, is perpetual motion. If I find perpetual motion, I do not see the boundaries of human creativity... you See, my good Martyn! To make gold - task enticing opening, can be interesting and profitable, but to find a perpetuum mobile... Oh!...”.

Were invented hundreds of “perpetual motion”, but no one moved. In each case, as in our example, the inventor has lost sight of any circumstance which had destroyed all the plans.

Here's another example of seeming perpetual motion: the wheel from rolling in it heavy balls.


Imaginary eternal engine roll the balls.


The inventor imagined that the balls on one side of the wheel, being always closer to the edge, its weight will cause the wheel to spin.

Of course, this will not happen for the same reason as with the wheel shown in the previous figure. However, in one of the cities of America was arranged for advertising purposes, to attract public attention to a café, a huge wheel of exactly this kind.


Imaginary eternal engine in Los Angeles (California), arranged for the sake of advertising.


Of course, this “perpetual motion” discreetly operated skillfully hidden by an external mechanism, though the audience seemed wheel drive rolling in the slits heavy balls. In the same way there were other imaginary samples eternal engine, exhibited at one time in the Windows of watch stores to attract the audience: they are all invisibly set in motion by an electric current.

One advertising “perpetual motion” gave me once a lot of trouble. My students-workers were so impressed, that was cold to my evidence of the impossibility of perpetual motion. Kind of balls, which, rolling, rolling wheel, and the same wheel went up, convincing them stronger my arguments; they didn't want to believe that the so-called mechanical miracle is driven by electric current from a city network. Rescued me that in weekend the current was not applied. Knowing this, I advised the students to go to the window these days. They followed my advice.

"Well, have you seen the engine? I asked.

"No, " he replied sheepishly. - It is not visible: covered with newspaper...

The law of conservation of energy regained their confidence and no longer had lost it.

Entertaining physics J. Perelman


System Orphus


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