Perpetual motion -- nonsense for over 100 years

Mar 10 2010 Published by under ... the Hell?, History of science

Some two years ago, I wrote a post about a device called the "whipmag", a thinly-disguised perpetual motion machine based on magnets that would supposedly accelerate without an external source of energy once set in motion.  I was understandably critical of the device, and free energy has yet to reach the masses, but that doesn't stop people from being true believers.  Last week, I received the following comment on the post (written two years ago, mind you):

Neither the author of this article nor the guy in the second video actually gives any data or analysis applicable to the device in the first video. The author’s diagram does not reflect the structure of the device in the video. Also the author mentions several times “conservation of energy” and “thermodynamics” laws, but does not apply those concepts to explain how the device could not work. Thus no analysis has taken place in this article, only emotional oversimplification ( just like the second video guy ) and a trail of distracting mini history lessons.

The complaint seems to be that I don't actually spend my time proving that the device can't work.  My answer to this is that I don't have to!  At this point, such devices have been debunked so often and the laws of physics so well understood that the onus is on any would-be perpetual motion discoverer to demonstrate that their device does work, and ideally explain why.

It is especially amusing to hear criticism of "mini history lessons".  Science is a process which builds upon all knowledge that has come before; what we have discovered previously -- scientific history -- is crucial.  It would be impossible for science to progress if we spent all of our time, in the absence of new evidence, testing schemes that we know have already failed.

With that in mind, it is worth pointing out that perpetual motion has been considered impossible -- and treated with scorn -- for a long, long time.  When I dug up the first volume of The Harmsworth Magazine, dated 1899, to seek out a story by Winston Churchill, I also found a popular article on perpetual motion. It is not kind to the concept, or the people who pursue it.

There isn't very much information on The Harmsworth Magazine online.  It was started in 1899 by British newspaper magnate Alfred C. Harmsworth, founder of the Daily Mail, and evidently run by his brother Cecil.  As to the purpose of the magazine, it is perhaps best to quote Harmsworth himself, from the introduction to the first issue:

Together with a great many other people. we came to the conclusion long since that a good deal of the literary wares that are foisted on the public by means of the ordinary advertising methods of personal paragraphs and "interviews" is mainly rubbish. Frankly and openly do we, therefore, declare that mere "names" will never command an entrance to the pages of this Magazine. As with our "Daily Mail" and our other journals, we shall rely on new writers. The public is weary of the reiteration of the same contributors to each of the monthly publications. He and she wants something new. It is our desire, for the sake of the public, for the benefit of young artists and others, and for our own profit, to avoid the productions of the professional "ring" of much advertised mediocrity which most assuredly dominates many of our Magazines to day, though the work of really representative men and women will always be secured, without regard to its cost.

The goal seems to have been the creation of an upscale "Reader's Digest", combining both fiction and nonfiction articles, with lavish illustrations to boot! The format may not have been particularly successful, as the magazine was renamed the London Magazine in 1900, after only three volumes.

There are a number of popular science articles in the first volume, including the one I'm interested in, " 'Perpetual motion' seekers: their fascinating but hopeless pursuit."  Curiously, the author of the article is not given, which is almost unique in the magazine.  Perhaps this is simply because it was written by a staff writer, or perhaps the author wanted anonymity due to the rather harsh tone taken.

The article does not start kindly:

Three apparently hopeless quests have engaged the abilities of inventors and scientists from a very early period -- the Philosopher's Stone, that should convert everything it touched into pure gold; the Elixir of Life, that once partaken of should invest the recipient with immortality on earth; and Perpetual Motion.

To the average man it is a self-evident fact that unless you put energy or force of some sort into a  machine it won't work.  Thus, a locomotive will not move unless you apply steam or electricity, nor a bicycle unless the muscular energy of your own body propels it.  But, simple as this fact may seem, there have been, from early times, as we have indicated, men whose whole object in life has been to construct a machine that, once started, shall run for ever by its own momentum.  There are such people to-day; and it is pathetic to think what an immense amount of inventive genius has been expended on projects that we may declare to be absolutely hopeless of achievement, even in these days of phonographs and wireless telegraphy.

Ouch.  The author of the post also doesn't feel the need to debunk individual contraptions in detail:

"Why can't it be done?" says the Inventor.  Many reasons to the contrary might be adduced, but the most cogent answer to the practical man lies in this great fact, that up to the present not a single perpetual motor has ever yet been seen at work -- that is to say, no machine has ever yet been invented which, when once started, would work for an indefinite time without a corresponding amount of energy being given it.

Careful experiment and daily observation all point to one comprehensive principle -- that you cannot get out of a machine more work than you put into it.  In the locomotive, for example, the work given out when it is in operation is exactly equivalent to the energy stored up in the inert coal cast into the furnace.  Although this principle in all its scientific exactitude is less than a century old, yet its truth is now so well settled, that nothing short of an actual working perpetual motor could demonstrate its falsity.  The search for the Philosopher's Stone, the production of an Elixir of Life, have, like the hope of an El Dorado, been consigned to the limbo of forgotten things.  Nevertheless, in spite of science, aspirations after the Perpetual Motor still burn fitfully.

This is an interesting point: some crackpot fantasies seem to have fizzled and faded with time and increasing knowledge, while others, like perpetual motion and creationism, stay somewhat constant.

Some, indeed the vast majority, of the chimerical methods for getting work for nothing, are being rediscovered day by day, and, as before, cast aside.  An almost incredible amount of wasted labour and fruitless effort have been devoted to this subject.  The quest, however, ever seems to be fresh and attractive, and year after year in wearying succession continues to allure, as the records of the Patent Office show, a never ending train of deluded enthusiasts.

It is worth reminding the reader that this article was written 110 years ago!  Even then, pretty much every supposed scheme of perpetual motion had been repeated and rediscovered ad nauseum.  Devices such as the "whipmag" are simply more elaborate versions of devices that were discounted long, long ago.

The remainder of the article is a description of some of the perpetual motion machines that have been concocted "recently".  A number of them are devices I had not seen before, and it is worth showing a few of the pictures:

This is a modern version of the "overbalanced wheel", which was apparently first conceived by Villard de Honnecourt, circa 1230 C.E.; in Honnecourt's defense, he lived in an era when people didn't know any better.  Compare Honnecourt's wheel, pictured below, to its modern successor:

The supposed "principle" of the overbalanced wheel is simple: the weights are designed to extend further from the center of the wheel on on side than on the other.  This superficially would seem to create a torque imbalance, which means the side with the extended weights will be pulled downward.  As the wheel turns, the extended weights retract and the retracted weights extend, presumably repeating the cycle.

We can make a simple argument against the success of this device using the principle of energy conservation and the symmetry properties of the wheel.  To simplify matters, let us assume that the device returns to its starting configuration after it rotates an angle $latex \theta$, as illustrated below:

Assuming we start our machine at rest, it starts with a certain amount of gravitational potential energy.  The total energy is the combination of this gravitational potential energy and the kinetic energy, i.e. the energy of motion.  Assuming the wheel starts turning when we let it go, its potential energy lowers as its kinetic energy increases -- this is "energy conservation".  However, when the wheel has rotated an angle $latex \theta$, it has exactly the same configuration as when it was released.  This means that the potential energy must be exactly the same as it was in the first position!  If we assume the best possible scenario -- the potential energy was a maximum when we let the wheel go -- this implies that some intermediate position over that angle $latex \theta$ is a minimum of potential energy, i.e. an equilibrium point of the wheel.  When we release our wheel and let it start to spin, at best we expect it to rock between its original position and the position an angle $latex \theta$ away, before friction reduces its motion to nothing at the equilibrium point.

This is a bit of an oversimplified explanation; for instance, the moving masses on the wheel do not necessarily have the same position after rotating $latex \theta$.  However, one can see that other positions of the masses will tend to slow the motion of the wheel -- for instance, if the masses are extended on the right side of the wheel, they will balance the left side of the wheel better and counteract any force.  More elaborate "overbalanced wheels" have essentially the same problem, only hidden better with increasing complexity.  The "whipmag" fails for the same reason.

The net result is that energy conservation automatically implies the nonexistence of perpetual motion.  This, however, did not and does not deter enthusiasts from their attempts.  Taking a look at some other devices from the article, we have:

The grindstone machine is just another overbalanced wheel: the idea is that half of a wooden block is submerged in water, while the other half is in air.  The submerged half should float, creating a net spinning of the grindstone.

From an energy perspective, one can see why this fails.  The system has exactly the same potential energy no matter what position the grindstone is in, and there is therefore no position that allows the release of potential energy into kinetic energy.

Here is one more machine from the article that is worth pointing out for its misguided cleverness:

Allow me to quote once again from the article to explain this device:

Another favourite scheme is to employ the well-known property of liquids to rise of their own accord against the force of gravity when in microscopic channels, such as are found in all porous bodies, this property of rising being due to what is known as "capillary attraction." For instance, it is a matter of every-day observation that oil ascends a wick, water passes up over the edge of a basin through a towel which, partially immersed in the water, hands over the side.  Some idea of the enormous power of this property of ascending is given by a celebrated French savant who has found that capillary action is capable, under favourable circumstances, of exerting a pressure four or five times as great as that of the atmosphere, and who thinks this is largely efficient in promoting the ascent of sap in plants.  Consequently, if this natural uprising property of liquids could be only laid hold of, the problem of getting work for nothing, so thinks our schemer, would thereby be solved.  We have selected for illustration a form of apparatus where, on thet left, a bundle of flexible sheets is placed almost in contact, so that the liquid into which they are dipped rises in the microscopic spaces between them.  This provides a "head" of water, which is expected to overbalance the right hand of the system, where the sheets have been separated by the wires of a grid, or other equivalent, so as to destroy the capillary action on that side.

I'll leave it to the reader to come up with an explanation as to why this machine fails; feel free to post your hypotheses in the comments!

Other tools of the perpetual motion enthusiast's toolkit have changed little over the years:

The propounder of perpetual motion theories does not always confine himself to diagrams, but sometimes deludes himself in a cloud of verbiage.  Here is a sample.  "Let us," says the theorist, "construct a wheel of immense dimensions.  On one side of it, let there be hung a huge mass.  On the opposite side suspend innumerable small weights.  Then shall it be found that the wheel will continually revolve.  For when the huge mass is at the top, its weight will cause it to descend.  Why is this?  The answer is obvious -- because it is so heavy.  In the meantime the innumerable small weights will reach the top, and thereupon they will descend.  Why is this?  The answer again is clear -- because there are so many."

Hopefully the description of this article -- published over 100 years ago in a popular magazine, not a scientific one -- makes it clear why modern-day physicists do not feel the need to debunk specific perpetual motion schemes anymore.  Energy conservation is firmly established, and has been for at least 150 years, in terrestrial physics, and no "free energy" scheme based on simple mechanics or electromagnetics is going to overcome this principle.

One wonders why, in spite of this evidence, people still try and construct perpetual motion machines.  One way to think of it is that the enthusiasts confuse the disciplines of physics and engineering -- they treat fundamental physics laws as obstacles that can be overcome with just the right amount of "tweaking".  When building an airplane, for instance, the difference between flying and crashing can depend on very subtle design issues such as the shape of the wing, the distribution of weight, and so forth.  However, manned flight is not impossible according to the laws of physics, while violation of energy conservation is.

Let me end with one more device from the article, and its description:

The description from the article:

At the present time the public mind is so greatly agitated on the subject of horseless vehicles, that an illustration of the perpetual motionist's ideas on the subject is given.  Here the weight of the vehicle and its occupants bears upon water in cylinders supported on the wheels.  The pressure produced in the water in this way is conveyed by means of pipes to the back of the carriage, where it is employed to push the vehicle along.  Such speed the inventor in this case expected to obtain, that, with great forethought, he has provided a "cow-catcher" at the front, by means of which unfortunate persons who inadvertently get in the way are to be gently waived aside.  Of course, the larger the number of people carried, the greater the pressure on the water, and hence, in the inventor's mind, so much greater the speed.

This one is a violation of another fundamental physics law besides energy conservation; I'll again leave it to people to explain in comments exactly what is wrong!

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