Perpetual motion?

[tut]

https://www.facebook.com/steve.winterbe ... 3283278696

[robin]

You can tell it is not perpetual. If you watch to the end of the video, it stops.

[tut]

He stopped it though by taking the weights off.

It still seemed to be going as strong as ever.

tut

[thinfourth]

I have seen many perpetual motion machines on the internet

Two things strike me about these machines that if left unattended will keep going until the heat death of the universe

1 They only ever have a demo video 30 seconds long

2 They always have a nice chunky base just slightly bigger then a RC car battery pack



And one must ask

What pulls down the middle of the balance beam after the ball has hit the end stop?

As it ain't gravity

[robin]

I am sure you can make a machine that goes on and on for a long time with no additional energy input; just that they always stop in the end due to friction. So the challenge in a perpetual motion machine is finding a way of proving it is that and not just a low friction machine, or a machine that benefits from the input of energy from the environment (solar, heat).

Consider the solar system; even without input from the rest of the universe, the planets are going to orbit the sun until the sun dies billions of years from now. Good luck videoing that and putting it on YouTube. It isn't a perpetual motion machine, though. Eventually the planets would stop orbiting anyway even if the sun were a solid lump of iron rather than a big reactor.

Cheers,
Robin

[BiggestNizzy]

Thermodynamics

[Ferg]

^^this. They're laws for a reason.

[tenkfeet]

He is wearing a convincing scientist jumper, must be true.

[robin]

Quoting thermodynamics is a cop out, though. The more philosophical point is how do you prove something is not a perpetual motion machine, given you allow the concept of a perpetual motion machine to exist. By the way, I am not sure that thermodynamics precludes the existence of a perpetual motion machine. It merely precludes the existence of one you can observe. Or a meringue?

Cheers,
Robin

[BiggestNizzy]

The second law of thermodynamics states that perpetual motion machines are epistemically impossible.

[tut]

I think the same, as far a we know from the present Laws of Physics you can not get something for nothing, and you can not exceed the speed of light.

tut

[robin]

It all depends on what you define as a system. Provided the system does no work there is nothing stopping it continuing to have motion.

After all, an electron will presumably "orbit" the atomic nucleus with which it is associated for ever (in an infinite vacuum). As soon as you interact with it, you take away (or add) some energy and things change.

[robin]

^^this. They're laws for a reason.

Funnily enough being "only" a law makes them weak by comparison to theories (laws fit empirical facts, theories are explanations of how things work that are then demonstrated to be true by repeated attempt to disprove them experimentally). Newton's laws of gravity remained valid for 100's of years because they fit the empirical data of the day; it turns out they are not valid if you test them elsewhere in the universe, e.g. near a black hole. So now they remain valid but only in the confines of a weak gravitational field. Thus it is easy to see a situation where the laws of thermodynamics become subject to some caveat and don't apply outside of those boundaries; they were constructed using empirical data from the universe as we know it (quite well, as it turns out so far, but you know how it goes - some smart arse always comes along with a bigger telescope ).

Anyway, I accept that a perpetual motion machine of the type typically shown on YouTube cannot work, nor can any machine do work forever without a source of energy.

I was really more interested in the philosophical question of how one would prove something *is* a perpetual motion machine (as opposed to proving it is not, which is the more conventional approach).

Cheers,
Robin

[steve_weegie]

^^this. They're laws for a reason.

I was really more interested in the philosophical question of how one would prove something *is* a perpetual motion machine (as opposed to proving it is not, which is the more conventional approach).

You use the same scientific method that all other proofs are subject to. You write a paper explaining how your machine works, also detailing where our current understanding of the physics fails. Others teams will peer review the work, build the machine in question, and try to replicate the findings while attempting to refute the central point.

Which, in this case, is that perpetual motion machines do not exist and someone left the electromagnet out of the schematics

Quantum mechanics is different and not subject to the laws of classical physics.

[tut]

My "you can not get something for nothing" is of course incorrect in one sense, as an object powered by sun, wind, etc is using natural energy that we do not generate ourselves, thus is a free source of energy.

Definitely the first use of "epistemically" Nizzy.

tut