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Perpetual motion machines
Topic Started: Jun 23 2011, 12:43 PM (602 Views)
CJ
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A very minor case of serious brain damage

I'm sure we've all heard of these. The idea of a perpetual motion machine is that, once you set it going, it can continue forever, without any outside source of energy (such as fuel). Sometimes, they are intended to produce more energy than they require to operate, so that this 'free energy' can then be used to perform useful work.

It sounds like we could use one right about now, to solve all the world's energy problems. Unfortunately, according to our current understanding of physics, they would be impossible, because such a machine would violate the First Law of Thermodynamics (which essentially states that in a closed system, the total energy remains constant). Many would also run into trouble with the Second Law of Thermodynamics (i.e. in a closed system, the net entropy must increase). It should be noted that saying that anything is completely impossible is unscientific: if, hypothetically, someone were to build a true perpetual motion machine, then it would just mean that the laws of thermodynamics were falsified. Let's face it, though: the laws of thermodynamics are so well founded that that just isn't going to happen in reality.

However, perpetual motion machines do have one perpetual quality: people perpetually invent them :P . Here are just a few:

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A lot of early ones (like these ones, designed by Leonardo da Vinci) were based on wheels. The basic idea was that the wheel contained a series of masses, which were free to move in some way. Those towards the top of the wheel would fall in towards the centre, and those towards the bottom would fall out away from the centre, and the resulting difference in torque would be able to keep the thing going forever. There were about a million different variants on this basic theme, none of which worked.

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This one was designed in the 17th Century by the Bishop of Chester, Bishop Wilkins. The idea was that there was a ramp with a big magnet at the top, and a small magnetic ball was placed on the ramp. The magnet would attract the ball up the ramp, but before reaching the top, the ball would fall through a hole, which would take it to the bottom of a ramp. Unfortunately, any magnet strong enough to attract the ball up the ramp would also take it right over the hole!

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This is a diagram of a machine built and exhibited by American inventor Charles Redheffer in the early 19th Century. As with many other perpetual motion machines that were put on public exhibition, this turned out to be a con: it was eventually discovered that there was an old man in the attic operating it constantly with a crank.

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Cox's Timepiece, which operates on changes in atmospheric pressure. It's sometimes thought of as a perpetual motion machine, but technically, it isn't, as it does use an outside energy source (albeit not one that is readily apparent).

So, do you have any favourite perpetual motion machines that you would like to discuss?
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lamna
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It's really sad to see on youtube, dozens of people who think if they just arrange magnets right that they will spin a motor all on their own. People waste huge amounts of money trying to do this.
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CJ
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A very minor case of serious brain damage

Yeah, they do :( . Quite apart from the thing about them wasting their money, it's also very sad that it's developed into its own brand of pseudoscience (although, with that said, it's been pseudoscience for almost 200 years now, at the very least).
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