Did I just think of a perpetual motion device?

The planets’ orbits are not perpetual. Orbits deteriorate over time.

No, pererual motion is impossible.

@The_Compassionate_Heretic
They deteriorate because of collisions with small particles in space. If these particles weren’t there it would go on forever.

My point is that I could write up an equation that describes perpetual motion, and not one that describes perpetual work.

So perpetual work is impossible. Is the saying just a misnomer?

You are assuming a frictionless environment. Perpetual motion would be easy if there were no friction.

I’m not a legitimate physicist but even I think that the planets orbits aren’t perpetual but are slowly spiralling.

But what do I know!

If you assume ideal conditions, you can easily come up with as many perpetual motion machines as you want. If you assume no friction, a turning wheel is a perpetual motion machine; if you assume perfectly elastic collisions, so is a bouncing ball. What makes perpetual motion impossible is that all real systems are chaotic to some degree, and because of this there is always a finite, irretrievable loss of usable energy; in other words, the second law of thermodynamics always applies. So you would have to ‘clean up’ the system to an impossible extent for this to work.

…..18 km/s [ 38,880 mph ] is about the velocity of the Sun relative to the Local Standard Rest Frame, ie. the speed of the sun relative to the other stars in our region of the Galaxy…. and our LSRF is moving even faster than that relative to the super massive black hole at the core of our Milky Way galaxy…....... our galaxy is slowly being consumed by the SMBH…....... this is also true for the Magellan galaxy which is reasonably close to us and is predicted to collide with the Milky Way galaxy some time… the net gravitational forces on us say for sure that the earth – sun combo is NOT a perpetual machine…. nor would be anything else you could think of !

@Jayne has the the right idea. Entropy is always increasing. You could create a system that seems, at first glace, to go on forever (from lack of friction, etc.), but eventually entropic effects from the motion of atoms would cause some loss of energy. After an eternity, it’s no longer moving. Second law of thermodynamics: you can’t break even.

The point I’m making is that the laws of physics aren’t broken with perpetual motion. You can have perpetual motion if and only if work isn’t being done.

You can never have perpetual motion in the real world because friction will always do work.

But even in a hypothetical world, you couldn’t have perpetual work.

My point is just that we should change the term.

@jackm….the laws of physics aren’t broken with perpetual motion because ‘perpetual motion’ does not exist….. hence you can say nothing further about it which could possibly make any sense…...... let it go !

@virtualist
I think your getting breaking the laws of physics, and not working in the real world confused.

@jackm As Jayne and I both said above, you still have the problem of entropy! Even in a perfect world with no friction, you will eventually lose energy to entropic effects, even if this happens incredibly slowly. So no, the laws of physics are still not broken.

Just to say as well, there is no ideal setting which does not have entropy. This is a fundamental issue that can not be removed for an ‘ideal’ system. It’s an issue with any system that involves physics.

I guess I never considered entropy a law that was on the same level as those other ones. It always seemed to me to more explain the real world.

i dont know maybe im just confused

…... an excellent link for those who want to know more about the absence of perpetual motion devices

a planet and star are not infinite in duration. so no.

@virtualist
According to that article, my machine is not impossible. Thats just the point I was trying to make. Motion should be changed to work.

That is an unfortunate article. The third kind is still impossible because of the second law. Entropy will force any system, eventually, to degrade. Any energy, when converted to a more chaotic one (such as work->heat) will take extra energy to convert back. And, in any system, regardless of how perfect, energy will be slowly converted to more chaotic forms. So, eventually, all energy will be converted to another, less useful form. And so, second law: you can’t break even.

Oh, and they give a bad example. superconductors are also not perfect systems, slight imperfections will result in the current being converted to heat very, very slowly. but it still happens.

True, there are some fluid dynamic effects (small eddy currents) of electrons in a superconductor that create entropy within even a perfect conductor.

@jackm There is no system that is not effected by entropy. Lets say we have an ideal situation where the only thing that exists is a planet and a star. The star emits radiation by fusing hydrogen into helium. The star loses mass and energy to entropy very slowly, but eventually it will collapse or explode altering the system.

The only possible example of what you are trying to explain would be two ideal gravitational bodies in motion. This idealized model assumes the bodies are perfect spheres assumed to be point masses, that no outside objects exist, and that the orbit is reversible. If you assume an ideal system of course you can come up with a perpetual motion machine; however, no such ideal system exists. The phrase “perpetual motion” is steeped in history, it would be rather hard to rename it. For the most part, people understand that “perpetual motion” relates to the idea of “free work.”

I’ve always considered the kind of system OP implies to be possible if you could provide a satisfactory vacuum, though it seems a lot simpler to store your kinetic energy in a spinning orb of dead matter.

Not perpetual motion, which is just cold fusion for chumps.

you can never have a perfect vacume so there is no such thing as a frictionless enviroment. (ie virtual particles, look it up)