Dak Posted January 12, 2008 Posted January 12, 2008 how is the earth not a perpetual motion thingy? what with it moving through space, presumably untill it desintegrates or the sun explodes? or is 'perpetual motion machine' more than just something that perpetually moves untill it breaks (i'm taking 'because it'll one day be destroyed' as a lame answre btw)
thedarkshade Posted January 12, 2008 Posted January 12, 2008 Earth is moving due to gravitation attraction!
YT2095 Posted January 12, 2008 Posted January 12, 2008 it will (and probaly IS) slowing down. it`s just so Massive that it`s hard to notice.
thedarkshade Posted January 12, 2008 Posted January 12, 2008 what do you mean to what, if you don;t mind to explain it more
Cap'n Refsmmat Posted January 12, 2008 Posted January 12, 2008 Earth is being slowed by friction from particles in interplanetary space, AFAIK.
Dak Posted January 12, 2008 Author Posted January 12, 2008 what do you mean to what, if you don;t mind to explain it more what is the earth being gravitationally attracted to? Earth is being slowed by friction from particles in interplanetary space, AFAIK. hmm... ok, if space were truly a vaccume, wouldn't the earth continue indefinately? or is a true vaccume impossible?
thedarkshade Posted January 12, 2008 Posted January 12, 2008 Centrifugal and Centripetal forces keep the planets together... It is the sun that keeps all the planets in their orbits because of the hight gravitational attraction that it exerts
YT2095 Posted January 12, 2008 Posted January 12, 2008 gravitationaly towards the Sun, but the motion is at a right angle to that so it stays in an orbit. and no even a Vacuum is subject to nuclear forces.
Sisyphus Posted January 12, 2008 Posted January 12, 2008 The laws of physics actually do allow for perpetual motion, and a planet orbiting in a true vacuum would be an example of it. What they don't allow for is getting out more energy than you put in. That's what most "perpetual motion machines" really are: sources of energy from nowhere, which is impossible. However, since in the real world you're always going to have "friction" of one kind or another (no truly closed systems, entropy, yatta yatta), in order to actually have perpetual motion, you would need a magical source of energy to make up for losses. So to summarize: there could be perpetual motion, there just isn't.
thedarkshade Posted January 12, 2008 Posted January 12, 2008 Actually you always get less energy than you put in...
swansont Posted January 12, 2008 Posted January 12, 2008 Basically it breaks down like this: if it's a situation where you could "run the movie" forward or backward and not know which is which, then the system could run perpetually — time asymmetry tells you if entropy is conserved or increases, and vice-versa. (there's also a weak interaction asymmetry that I'm not including here) Friction is one of those things that is time asymmetric. Anyway, the kinetic energy of the earth is huge compared to the losses, so it would take a long time to run down, but it's not perpetual.
Klaynos Posted January 12, 2008 Posted January 12, 2008 The laws of physics actually do allow for perpetual motion, and a planet orbiting in a true vacuum would be an example of it. What they don't allow for is getting out more energy than you put in. That's what most "perpetual motion machines" really are: sources of energy from nowhere, which is impossible. However, since in the real world you're always going to have "friction" of one kind or another (no truly closed systems, entropy, yatta yatta), in order to actually have perpetual motion, you would need a magical source of energy to make up for losses. So to summarize: there could be perpetual motion, there just isn't. Show me a true vacuum and I'll show you vacuum fluctuations It'd have to be a perfectly shielded vacuum as well, pesky EM fields get everywhere...
YT2095 Posted January 12, 2008 Posted January 12, 2008 ya forgot the Kasimir effect too oh yeah, AND Virtual particles!
Sisyphus Posted January 12, 2008 Posted January 12, 2008 Show me a true vacuum and I'll show you vacuum fluctuations It'd have to be a perfectly shielded vacuum as well, pesky EM fields get everywhere... I can't, because none exists. You know, like I said.
Riogho Posted January 12, 2008 Posted January 12, 2008 Earth is moving due to gravitation attraction! If the earth was moving only due to gravitational attraction we would be falling INTO the sun. Obviously we are not, we are falling toward the sun. View it as shooting a bullet in a horizontal direction while being on the earths surface, eventually it will plow into the ground due to graviational attraction because the velocity of the bullet is slowing down due to resistant forces. The earth was 'launched' from somewhere and if not for the gravitational attraction from the sun it would be going in a straight line.
foodchain Posted January 13, 2008 Posted January 13, 2008 how is the earth not a perpetual motion thingy? what with it moving through space, presumably untill it desintegrates or the sun explodes? or is 'perpetual motion machine' more than just something that perpetually moves untill it breaks (i'm taking 'because it'll one day be destroyed' as a lame answre btw) Perpetual motion as in infinite energy violates just about everything I think:D I have asked questions like this before on the boards also as in I don’t understand gravity all to well in relation to say a perpetual motion machine either. I would say the functions that lead to say solar systems or galaxies whatever that may be occurs over time of course in respects to say things like energy! Sort of like a thermostat. Of course issues like angular momentum change on say a quantum scale as in classical orbits would have the electrons falling into the nucleus, this however does not occur so then you have that whole deal with classical not being able to describe the quantum and so on which requires more experiments and so on. However I don’t think a vacuum or a BEC somehow destroys the interactions explained by the standard model, if that where true then I think nuclear reactions would be a lot more obtainable. Plus it would seem like planetary orbits are dynamic and can change of course.
MrMongoose Posted January 13, 2008 Posted January 13, 2008 perpetually moves until How can something be perpetual to a point?
Dak Posted January 13, 2008 Author Posted January 13, 2008 gravitationaly towards the Sun, but the motion is at a right angle to that so it stays in an orbit. and no even a Vacuum is subject to nuclear forces. ok... but, the entire solar system is moving in one direction? that's kinda what i was talking about (less so the orbiting) Basically it breaks down like this: if it's a situation where you could "run the movie" forward or backward and not know which is which, then the system could run perpetually — time asymmetry tells you if entropy is conserved or increases, and vice-versa. (there's also a weak interaction asymmetry that I'm not including here) Friction is one of those things that is time asymmetric. Anyway, the kinetic energy of the earth is huge compared to the losses, so it would take a long time to run down, but it's not perpetual. so, you'd have to completely get rid of friction? isn't there part of space that is 100% empty? 'beyond the boundries' of the bit of space that has 'stuff' in it? or is it not that simple? How can something be perpetual to a point? well, all it'd need is temporarily permenent motion. obviously. ---- ok, related question: what about all the movement that goes on in the universe as a whole? will that one day stop? or, will the movement 'spread out' through the unvierse till most things are travelling at the same speed? sorry if this all sounds crap btw, i've never really studied phisics or astrology
Sisyphus Posted January 13, 2008 Posted January 13, 2008 Perpetual motion as in infinite energy violates just about everything I think:D That is true, but that's not merely perpetual motion. Motion does not imply a change in energy. A steady orbit due to gravity would be perpetual motion, and would not require infinite energy, in theory. In practice, of course, there is always entropy which manifests itself in a variety of ways, but that is not related to the orbit itself. Taking away all other factors, there is no reason an orbit cannot continue forever. Of course issues like angular momentum change on say a quantum scale as in classical orbits would have the electrons falling into the nucleus, this however does not occur so then you have that whole deal with classical not being able to describe the quantum and so on which requires more experiments and so on. That's not really the reason. Classically, an electron orbit could continue indefinitely. so, you'd have to completely get rid of friction? Yes, basically. isn't there part of space that is 100% empty? No. In fact, quantum uncertainty means that nothing is 100% anything. well, all it'd need is temporarily permenent motion. obviously. I take you to mean a finite amount of time in which you end up in the same situation you started in. Right? Can't happen. ok, related question: what about all the movement that goes on in the universe as a whole? will that one day stop? or, will the movement 'spread out' through the unvierse till most things are travelling at the same speed? That is one of the possible ends to the universe, yes. See heat death of the universe. i've never really studied astrology I don't think that hurts...
swansont Posted January 13, 2008 Posted January 13, 2008 so, you'd have to completely get rid of friction? isn't there part of space that is 100% empty? 'beyond the boundries' of the bit of space that has 'stuff' in it? or is it not that simple? You'd have to get down to the atomic level and below to even get close. There is no "friction" in individual nuclear reactions — that's as close as you can come to having an elastic collision. Once you add in other forms of energy (e.g. photons), it's no longer a reversible system.
John Cuthber Posted January 13, 2008 Posted January 13, 2008 "That's not really the reason. Classically, an electron orbit could continue indefinitely." No it wouldn't. If it were orbiting in a circle it would be accelerating and accelerating charges emit em radiation. I think the belief among physicists is that a similar radiation (gravity waves) would be emited by, for example, the sun and earth and this would eventually dissipate the kinetic energy of the system. I think this remains theoretical because the effect is week.
thedarkshade Posted January 13, 2008 Posted January 13, 2008 Of course it's not 100% nothing. It's full of dark matter and intergalactic gas!
swansont Posted January 13, 2008 Posted January 13, 2008 "That's not really the reason. Classically, an electron orbit could continue indefinitely."No it wouldn't. If it were orbiting in a circle it would be accelerating and accelerating charges emit em radiation. I think the belief among physicists is that a similar radiation (gravity waves) would be emited by, for example, the sun and earth and this would eventually dissipate the kinetic energy of the system. I think this remains theoretical because the effect is week. The decay of binary pulsars has been observed, though, that's consistent with gravity waves being emitted.
Mr Skeptic Posted January 14, 2008 Posted January 14, 2008 The earth's rotation is slowing due to tidal effects. I don't know about its orbit, but I imagine that is also imperceptively changing too.
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