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Perputual Machines? Possible?

  1. Mar 16, 2009 #1
    Well you might know that perpetual machines violate the laws of physics but do they really. Well firstly Newton's first law of motion states that an object in motion stays in motion unless acted upon an outside unequal force. Most the time when we roll a ball or something it's usually stooped by the familiar force of friction and air resistance but it'll keep going if they weren't present. So what happens if we can take them away. Well air resistance is simple to take away all we have to do is take away the air (vacuum). But how do we take away friction? You probably can't fully avoid it but even 75 percent is good. Also, another force that's always present is gravity. Can we use gravity to create electricity? Maybe magnetic force? Recently i did an experiment with the conservation of momentum. What i did was, i took marbles hit one with the other and carefully measured the force i put in and the force that came out. Well, it should be the same but it loss some momentum in the collision and friction. Then i did the same thing except with magnetic balls and the force that came out was much larger that i put in. So, doesn't that violate the laws of physics or not? Wouldn't this make perpetual machines that produce more electricity then they use possible? Help!
  2. jcsd
  3. Mar 16, 2009 #2
    Many devices and setups which seem to violate the laws of physics only do so because a part of the system has been ignored.

    An object suspended in a gravitational field can indeed create electricity. This is the principle behind hydroelectric power plants. Potential energy is converted into a voltage with the use of a motor. But realize, that there is a fair trade-off involved. The water loses height, and thus, loses potential energy. Once it has fallen off the side of the dam, there is no way to raise it back up without using energy equal to the electricity generated.

    Friction doesn't really add anything to the situation. Friction, from a distant perspective, always appears to be a sink for energy. Your output energy is always going to be slightly less than your input, due to friction. But friction boils down to heat and other microscopic ways that energy has escaped your system without your detection.

    It's not hard at all to create a near-perfect vacuum. Keep in mind that perpetual motion does NOT mean that an object stays in motion. It is a consequence of the conservation of momentum a moving object will continue to move at its speed until perturbed. So a ball moving through space at a constant speed is NOT an example of perpetual motion. Oddly enough, neither is the phenomenon of superconductivity, where you can maintain a non-zero current in a wire without a battery at super-cold temperatures. Just like with the dam, it takes energy to get the electrons in the superconductor moving, but once they are, it takes no energy to keep them in motion.

    EDIT: You probably also want to limit your posts about perpetual motion. It's a common "crackpot" theme on these boards and spending too much time talking about it will get your thread locked.
  4. Mar 16, 2009 #3


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    If all external forces (like friction) were removed, the ball would continue moving. But this is not a machine. If you connected a machine to extract energy from the system, the ball would slow down and stop.

    Yes, one example is hydroelectric power.

    You're free to separate two magnets and then apply a machine to extract energy as they're drawn together again (for example), but you'll always end up putting more energy in than you extract.

    No, force is not conserved.

    Again, this doesn't violate any physical laws; a lever does the same thing. And if you found that the momentum changed, then you weren't working with a closed system (for example, you may not have accounted for the Earth's change in momentum).

    Machines can produce more electrical energy than they use, but total energy is always conserved.
  5. Mar 16, 2009 #4

    Doc Al

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    What do you mean by "the force you put in" and "the force that came out"? What did you actually measure?
  6. Mar 16, 2009 #5
    It is the failure of perpetual motion machines that provides some of the strongest evidence that energy is conserved.
  7. Mar 16, 2009 #6
    I measured the acceleration by making a grid (one centimeter is black, the other is white, then black and so on,,,). Then i got it on camera, put on the computer, and then slowed the footage down so that i could count how much it traveled and how long it took. What i meant by the force i put in, was the acceleration of the first marble, and the force that came out was the acceleration of the second ball after the collision. I sort of got the idea from the toy Newton's Cradle. I don't remember exactly what the numbers were but the acceleration of the second "magnetic ball" was about 2 times more.
  8. Mar 16, 2009 #7
    I know that talking about perpetual machines sort of makes you sound like a "crackpot" but as a little kid i used to think of ways that systems might create electricity without having to use fuel or whatever, hoping it'll stop climate change and make me a bit more richer. A word i often heared was "free energy" and while researching i stumbled upon the laws of thermodynamics and realized it wasn't possible. I don't ever think of perpetual machines anymore but I still thought that there might be a few "loop holes" and so i wanted to ask you guys.

    Also, you know how you said gravity drains potential energy and in order to get it back up you need the same energy again. And you guys also said in order to get energy from magnets you still need to add energy to put them together. What happens if you use gravity to put a magnet in motion and as it got closer to another magnet under neath it, they repel sending the original magnet up again then gravity pulls it down again and the magnet will put it up again and so on,,,. If you can make that a controlled system can you create a perpetual machine? Again i don't want to sound like a crackpot.
  9. Mar 16, 2009 #8
    You might want to look up Harmonic Oscillator on Wikipedia. It's not exactly the situation you describe, but it fits the phenomenon you seem to be thinking about. In a harmonic oscillator, a weight is attached to the end of a frictionless spring. The spring pulls on the weight with a force proportional to how far it is stretched (that is, proportional to the weight's displacement). Under perfect conditions, the weight will swing back and forth in a sinusoidal motion ad infinitum. The motion of the weight is constantly changing, but energy is still being conserved. At any point in time, if you take the kinetic energy of the weight and the elastic potential energy of the spring, they will add up to a constant number. Yet the weight is constantly undergoing a change in its motion.

    Is this far fetched? Not at all. The same thing happens with planets orbiting a star. Their speed (in a perfect circular orbit) remains constant, but their direction of motion is always changing. That constitutes an acceleration. But it's pretty easy to see that stable orbits do not violate conservation of energy. The kinetic energy only depends on the speed of the object, not its direction, so there is no loss or gain of kinetic energy. And since the planet maintains the same radial distance from the star, it does undergo a change in gravitational potential energy either.
  10. Mar 16, 2009 #9
    So does it ever stop and can you create electricity from it?
  11. Mar 16, 2009 #10
    You can. But watch what you're doing! If you throw a motor inside of a stable oscillating system, you can create a voltage. However, as you do, the oscillation will decay. You created the electricity... but from what? From the weight's kinetic and potential energies. The more energy you siphon off, the less energy your weight has to move, and it slows to a stop, and your electricity runs out.
  12. Mar 16, 2009 #11
    There are no loop holes in our current physical theories (standard model + general relativity) but there is one giant loop hole: our curent physical theories are not complete, and they may not yet account for some important phenomena. If you really want to build a perpetual motion machine you should work on theories of quantum physics beyond the standard model. With only classical physics e.g. Newton's laws, classical electromagnetism, Earth's gravity, etc there is no hope of finding a perpetual motion machine.
  13. Mar 18, 2009 #12
    It is important separating "Perpetuum Mobile" 1:st kind (PM1) and 2:nd kind (PM2).

    To me PM2 (getting mechanical power from heat energy in an equal temperature surrounding) must be just an engineering task to accomplish. Already the famous "Drinking Bird" working from evaporating water, could be regarded as PM2, if you regard water as a free source. Those maintaining it is not a PM2 because of the difference in temperature at evaporating surface cannot be serious - because that difference is created by the system itself. At least I think "Drinking Bird" illustrates the practical possibility of PM2 - although not a very efficient solution.

    Regarding PM1, I agree such should not be possible creating from known physics laws. Those laws are derived fulfilling conservation laws. But some kinds of "worm-holes" may well exist. History (if not every day experience) show us how easily we are mistaken - where the most obvious may be proven wrong.
  14. Mar 19, 2009 #13


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    On that note, we are done here. Please note for future reference that discussion on perpetual motion (over unity or not) is NOT allowed on PF, per the PF Guidelines.

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