6 ms·

Doesn't inertia guarantee the possibility of linear perpetual motion?

jacquesm 10y ago
No because there is such a thing as the heat death of the universe, which with the knowledge we have at present seems to be the most likely end-game. In other words: planets and comets will eventually completely disintegrate because their component atoms and even the components of those atoms will possibly disintegrate. You're looking at 10^30 years or so, so don't wait up for it, but it is still substantially shorter than 'forever'.
- Dylan16807 10y ago
  That is such a pedantic and irrelevant answer.
  - jacquesm 10y ago
    Given the context (planets and comets) it actually isn't. Planets are just like clocks, slowly winding down, especially the ones with moons through tidal friction. And even that weren't the case the long run will still get you. The problem with anybody proposing some kind of perpetual motion device is that perpetual really means 'forever', so no cheating. If you want to change the scope you can do so but you'll have to drop the 'perpetual' bit.
    - Dylan16807 10y ago
      If it lasts as long as the universe as we know it, I'm happy to call it 'perpetual'.
      - jacquesm 10y ago
        That's the trouble with definitions. The way I look at it is the spin-down of planets and the heat death of the universe are reduction to extremes arguments about why perpetual motion machines won't work. That's the very best you could do, in practice any 'perpetual' motion machine that is actually built will do enormously worse, so much worse in fact that I feel pretty confident placing the word between quotes. The problem with this subject matter is that it brings the kooks out of the woodworks like not much else does (oh, maybe 'over unity energy', en even more absurd concept). Of course any practical failures are due to insufficient funds or skill, and any theoretical limitations are just that: theoretical. But so far in spite of there being in excess of a million dollars of prize money awarded for the first perpetual motion machine nothing seems to have passed the first level of testing.
        Dylan16807 10y ago
        "The very best you could do" is downright simple if you can afford a big rocket. I think it's fine to admit perpetual motion non-machines where perpetual means 'longer than the universe has existed', and to focus on the important part that there's no perpetual energy extraction. A handheld box that outputs 1kW constantly for 2 billion years is very impossible despite bypassing all those arguments about eventual tidal/orbital/proton decay.
        jacquesm 10y ago
        No, big rockets will return to their point of origin eventually. Compare with a comet, which also re-appears every so many years. The only thing we've managed to launch into inter-stellar space are the Voyager craft and they are simply coasting, like any other bit of inter-stellar debris, straight-line unless captured by some gravitational field. And they'll run out of power within a decade. > A handheld box that outputs 1kW constantly for 2 billion years is very impossible despite bypassing all those arguments about eventual tidal/orbital/proton decay. It is impossible in principle, but if it were possible chances are that it would still not be a perpetual motion machine, likely it would be producing an excess of 1KW and be capped at that much output to mask the eventual running down of whatever power source sat inside the box. Applying all this to perpetual motion, it does not mean 'straight line unless interfered with', it means 'able to change configuration or acellerate relative to it's own frame of reference'. Dead objects are dead, whether they are moving respective to Earth or not is not relevant and does not magically make them perpetual motion machines, that's just energy imparted at some point in the past.
        Dylan16807 10y ago
        > Voyager Yes, that's what I mean by 'big rocket'. >It is impossible in principle, but if it were possible chances are that it would still not be a perpetual motion machine, likely it would be producing an excess of 1KW and be capped at that much output to mask the eventual running down of whatever power source sat inside the box. I meant something that is uncapped and does not run down. Just because it eventually breaks does not stop it from being a perpetual motion machine. Nobody claiming to have a perpetual motion machine is saying it will never need maintenance. An argument that everything needs maintenance is not enlightening. What matters is whether the energy source is infinite, not whether physical durability is infinite. > Applying all this to perpetual motion, it does not mean 'straight line unless interfered with', it means 'able to change configuration or acellerate relative to it's own frame of reference'. > Dead objects are dead, whether they are moving respective to Earth or not is not relevant and does not magically make them perpetual motion machines, that's just energy imparted at some point in the past. Did you forget that this line of conversation started with "Doesn't inertia guarantee the possibility of linear perpetual motion?" They're not talking about a machine with infinite power, they're talking about a dead perpetual motion non-machine.
fmihaila 10y ago
Linear perpetual (unaccelerated) motion is the same thing as no motion.
- 2_listerine_pls 10y ago
  Are you saying motion == acceleration?
  - aetherson 10y ago
    He's making the point that relativity says that if something is "in motion" but never accelerates (including accelerating by turning), you can just put your point of reference with that object and define it as "at rest." In practice, in the real universe, everything is subject to acceleration. You can only have an object that is infinitely moving without accelerating in a toy universe with only one object. At which point it is probably more intuitive to define it as at rest instead, since there's nothing else around for it to be moving in relation to.
    - 2_listerine_pls 10y ago
      I understand that everything is motionless (with respect to itself). However, we are talking about motion. So, it is obvious that there is an implicit frame of reference other than the object itself. It makes no sense for him to bring up that everything is motionless.
      - jacquesm 10y ago
        It makes perfect sense. Maybe not to you, but all motion is relative to some frame of reference. So if there is no acceleration in any dimension an object might as well be at rest until it collides with something (which would show either one or both objects to be in motion relative to a third reference frame). The universe does not have convenient 'true' grid lines along its axis to indicate the one true reference frame. You would be hard pressed to indicate a frame of reference that is motionless compared to everything else.

No because there is such a thing as the heat death of the universe, which with the knowledge we have at present seems to be the most likely end-game. In other words: planets and comets will eventually completely disintegrate because their component atoms and even the components of those atoms will possibly disintegrate. You're looking at 10^30 years or so, so don't wait up for it, but it is still substantially shorter than 'forever'.

Dylan16807 10y ago
That is such a pedantic and irrelevant answer.
- jacquesm 10y ago
  Given the context (planets and comets) it actually isn't. Planets are just like clocks, slowly winding down, especially the ones with moons through tidal friction. And even that weren't the case the long run will still get you. The problem with anybody proposing some kind of perpetual motion device is that perpetual really means 'forever', so no cheating. If you want to change the scope you can do so but you'll have to drop the 'perpetual' bit.
  - Dylan16807 10y ago
    If it lasts as long as the universe as we know it, I'm happy to call it 'perpetual'.
    - jacquesm 10y ago
      That's the trouble with definitions. The way I look at it is the spin-down of planets and the heat death of the universe are reduction to extremes arguments about why perpetual motion machines won't work. That's the very best you could do, in practice any 'perpetual' motion machine that is actually built will do enormously worse, so much worse in fact that I feel pretty confident placing the word between quotes. The problem with this subject matter is that it brings the kooks out of the woodworks like not much else does (oh, maybe 'over unity energy', en even more absurd concept). Of course any practical failures are due to insufficient funds or skill, and any theoretical limitations are just that: theoretical. But so far in spite of there being in excess of a million dollars of prize money awarded for the first perpetual motion machine nothing seems to have passed the first level of testing.
      - Dylan16807 10y ago
        "The very best you could do" is downright simple if you can afford a big rocket. I think it's fine to admit perpetual motion non-machines where perpetual means 'longer than the universe has existed', and to focus on the important part that there's no perpetual energy extraction. A handheld box that outputs 1kW constantly for 2 billion years is very impossible despite bypassing all those arguments about eventual tidal/orbital/proton decay.
        jacquesm 10y ago
        No, big rockets will return to their point of origin eventually. Compare with a comet, which also re-appears every so many years. The only thing we've managed to launch into inter-stellar space are the Voyager craft and they are simply coasting, like any other bit of inter-stellar debris, straight-line unless captured by some gravitational field. And they'll run out of power within a decade. > A handheld box that outputs 1kW constantly for 2 billion years is very impossible despite bypassing all those arguments about eventual tidal/orbital/proton decay. It is impossible in principle, but if it were possible chances are that it would still not be a perpetual motion machine, likely it would be producing an excess of 1KW and be capped at that much output to mask the eventual running down of whatever power source sat inside the box. Applying all this to perpetual motion, it does not mean 'straight line unless interfered with', it means 'able to change configuration or acellerate relative to it's own frame of reference'. Dead objects are dead, whether they are moving respective to Earth or not is not relevant and does not magically make them perpetual motion machines, that's just energy imparted at some point in the past.
        Dylan16807 10y ago
        > Voyager Yes, that's what I mean by 'big rocket'. >It is impossible in principle, but if it were possible chances are that it would still not be a perpetual motion machine, likely it would be producing an excess of 1KW and be capped at that much output to mask the eventual running down of whatever power source sat inside the box. I meant something that is uncapped and does not run down. Just because it eventually breaks does not stop it from being a perpetual motion machine. Nobody claiming to have a perpetual motion machine is saying it will never need maintenance. An argument that everything needs maintenance is not enlightening. What matters is whether the energy source is infinite, not whether physical durability is infinite. > Applying all this to perpetual motion, it does not mean 'straight line unless interfered with', it means 'able to change configuration or acellerate relative to it's own frame of reference'. > Dead objects are dead, whether they are moving respective to Earth or not is not relevant and does not magically make them perpetual motion machines, that's just energy imparted at some point in the past. Did you forget that this line of conversation started with "Doesn't inertia guarantee the possibility of linear perpetual motion?" They're not talking about a machine with infinite power, they're talking about a dead perpetual motion non-machine.

fmihaila 10y ago

Linear perpetual (unaccelerated) motion is the same thing as no motion.

2_listerine_pls 10y ago
Are you saying motion == acceleration?
- aetherson 10y ago
  He's making the point that relativity says that if something is "in motion" but never accelerates (including accelerating by turning), you can just put your point of reference with that object and define it as "at rest." In practice, in the real universe, everything is subject to acceleration. You can only have an object that is infinitely moving without accelerating in a toy universe with only one object. At which point it is probably more intuitive to define it as at rest instead, since there's nothing else around for it to be moving in relation to.
  - 2_listerine_pls 10y ago
    I understand that everything is motionless (with respect to itself). However, we are talking about motion. So, it is obvious that there is an implicit frame of reference other than the object itself. It makes no sense for him to bring up that everything is motionless.
    - jacquesm 10y ago
      It makes perfect sense. Maybe not to you, but all motion is relative to some frame of reference. So if there is no acceleration in any dimension an object might as well be at rest until it collides with something (which would show either one or both objects to be in motion relative to a third reference frame). The universe does not have convenient 'true' grid lines along its axis to indicate the one true reference frame. You would be hard pressed to indicate a frame of reference that is motionless compared to everything else.