Perpetual Motion Machine... or next best thing?

Not sure if this YouTube Video has been brought up here or not,* but at face value it looks like someone has contrived a magnetic/mechanical device that, with a few flips of the wrist, will eventually get a flywheel to spin pretty fast and for what seems like would last a long time sustained by magnetic repulsion/attraction (I assume).

Is this the penultimate PMM, so to speak? Is there anything ruling out a device that while may not sustain itself forever, but will last a long enough time to make itself useful?

*Not ruling out the fact that this may be a hoax, or if not, that the effect doesn’t last long enough to be useful. I am full aware what the 1st & 2nd laws of thermodynamics has to say about this.

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Yes…the laws of thermodynamics prevent it from being useful. In short you will always need to put more energy in than you can get back out.

So, even if this device were able to overcome the resistance and friction inherent in its design, and were able to last for a full day, wouldn’t that be enough to charge a battery, for example?

ETA: I see, eventually the magnets will demagnetize. Even if it’s incredibly efficient… there’s the “cost”.

No. In order to charge a battery, you have to use the rotation to generate an electric current. That generation imposes its own load, over and above the normal frictional losses.

Ah, I did not know that. Thanks Robot Arm.

What’s that supposed to mean? :dubious:

-FrL-

This is sort of similar to an old thought experiment: Say you put a coil of wire in a frictionless environment, like outer space, beyond the measurable reach of any gravitational field. Then you stick a magnet inside (but not touching) the coil, and spin it. Then you attach the coil to a light bulb to observe if any current is generated. Will the light bulb shine forever? After all, there is no friction to slow the generator down.

In this type of thermodynamics conundrum, it often helps to think of the problem backwards. Energy, in the form of light, is coming out of the light bulb and into space. That energy comes from the coil, which is conducting an electrical current because the magnet inside is spinning. We know that we put a finite amount of energy into that magnet when we spun it. Logic dictates that eventually, that supply will be exhausted, somehow. So even if we don’t know exactly why, we might conclude that the magnet will slow down anyway, even though there’s no friction.

As it happens, the load placed on a generator (our light bulb) does exactly that. It creates an opposing magnetic field, which pushes the magnet in the opposite direction of its rotation. The result is that the magnet slows down.

Only that, no matter what kind of device or motor you build, there’s going to be some resistance. Obviously, an engineer will try to mitigate that, so he can eek out as much as possible from the energy source. In this case, he’s using some weird configuration of magnets, then spinning one in the opposite direction. I don’t pretend to understand it at all, but I was wondering if it’s possible to get the resistance and friction so low as to be almost negligible.

But then friedo explains why even with zero friction, the system will eventually wind down.

I shouldn’t have used the phrase perpetual motion. Gets a lot of people riled. After viewing the video, I simply wondered if the inventor hit on a novel way to use magnets to keep the flywheel going way more efficiently than any other attempt in this fashion.

At some science museums, you can pedal a bicycle attached to a generator. When a 200W light bulb is attached as a load, it becomes really hard to pedal.

I simply wondered if he didn’t have a little motor and battery under the flywheel.

Eek!!

I wondered that too.

There are two possibilities:

1. The thing has no active power source and will eventually stop spinning.

or

1. There’s an active power source spinning it.
Either way, it is not a PMM. So there’s nothing to see here.

Looks rather fraudulent to me. One of the comments is interesting - claiming that the band of silver tape on the spinning wheel is used to time a pulsed electromagnet, which is really what’s making it spin.

That’s actually the sound of an engineer trying to EEK out a living!

No wonder. Allowing for energy losses, you’re probably having to crank out half a horsepower to light a 200W bulb, maybe more. That’s a non-negligible load even if you’re a horse. (1HP ~ 735W)

He clearly claims that the wheel accelerates without any external power applied. What the inventor has hit upon is a way to use online video as a way to trick some people into thinking he’s invented a perpetual motion machine.

Our understanding of thermodynamics rules such a device out, but of course our understandings of all physical and technical phenomena are tentative in a way, and no doubt the future has many amusing surprises for us. So, it is not trivial to rule out free energy machines based on our present understanding, even if it is practically safe to do so.

However, as another point, if there actually were a source of free energy, how likely is it that its debut to the human race came about through word-of-mouth and YouTube videos?

More likely we would find out by a very large flash and the elimination of a major city.

Or a newspaper article about the machine’s theft by SPECTRE.