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Can energy be taken away from an object without touching it?

  1. Oct 18, 2013 #1
    The title isn't exactly accurate in describing what I am after.

    There is a ball moving along the ground, it was given an initial impulse, and now it is moving following conservation of momentum, gravity, air-resistance, friction, etc...

    If I wanted to take the energy from that rolling ball with say a gun-shaped device, the ball stops rolling and that energy is in my gun now. How could that be possible in real life?

    Then the energy could be applied to other objects whether they are moving or not.
  2. jcsd
  3. Oct 18, 2013 #2
    Hmm,I am not physic, I am just student so maybe that which I will say is stupid.
    I think that if you take the energy of an object,this object will lose whole his mass.
    E=mc^2 => 0=mc^2 => m=0.
    I am not sure about that I said,so please if someone knows more from to,to correct me.
  4. Oct 18, 2013 #3


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    It is rather unclear on what exactly you are asking here, especially this part: "If I wanted to take the energy from that rolling ball with say a gun-shaped device, the ball stops rolling and that energy is in my gun now. How could that be possible in real life?"

    If you are asking how we can harness the energy of "moving" objects, then I'll show you a windmill.

  5. Oct 18, 2013 #4


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    I think he is asking this:How to take the energy(kinetic maybe.) from a (moving) object using a gunshaped device from a distance.Store it and shoot it to a non-moving object far away to make it move.

    I think it's not possible in real life
  6. Oct 18, 2013 #5


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    What is a gun-shaped device, a gun (shooting projectiles) or a thing shaped like a gun? (this micrometer is shaped like a gun :smile:)

    I assume you mean a gun-like device shooting some sort of projectiles, but it would be better if you are more specific.

    You could check out

    but I'm not sure what you exactly meant, so it would be better if you are more specific.
  7. Oct 18, 2013 #6
    wormhole gun + 100% efficiency spring.
    gun creates wormhole in front of ball ball runs into spring on other side of wormhole. kinetic energy stored in spring. use gun to create wormhole behind object with no motion, release spring, kinetic energy transferred to new object.

    this is not possible with current technology.

    [|||]D cheers
  8. Oct 18, 2013 #7
    laser cooling is the answer !
    you basically hit an atom with a blue shifted photon * the photon is blue shifted because the atom is moving closer to the source of the photon * ( the real photon is not blue , its has an energy less than that of the blue , but it appears blue due to the doppler shift )
    the atom keeps releasing photons with energy higher than the energy of the photons that hit in the first place
    thus it keeps losing energy , until its motion becomes close to absolute zero , where it's movement is really slow the doppler effect is not noticeable any more
  9. Oct 18, 2013 #8


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    And how does this store the released energy in the gun/laser? That WAS the question, you know.
  10. Oct 18, 2013 #9


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    I don't know how laser cooling would work on a macroscopic object like a ball...

    And anyway, he wants the absorbed energy to be in his remote device now. Not possible with our current understanding.
  11. Oct 18, 2013 #10


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    This makes me remember 'despicable me'.Making the moon go small by a gun-shaped device.
  12. Oct 19, 2013 #11


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    The ball would need to emit light in the direction of its travel to stop rolling. Then the gun would have to collect the light.

    If the ball was a 1 kg object rolling at 100 m/s then it would have 5000 J of KE. But, more importantly, it would have 100 kg m/s of momentum. In order to stop it would need to emit light with 100 kg m/s of momentum, which corresponds to about 30 GJ of energy (~7 tons of TNT), or the complete conversion of .33 mg of mass into light.
  13. Oct 19, 2013 #12


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    Load a greased midget with spiked shoes, a fishing pole, a wad of chewing gum and a long leash around his neck into a miniature gun-shaped catapult. Launch him behind the rolling ball. The midget jams his cleats into the ground, puts the chewing gum onto the lure and casts, hitting the ball. As the line pays out from the reel, it runs a tiny generator, charging a battery cleverly tucked into the shaft of the fishing pole. When the rolling ball has come to rest its kinetic energy is now stored in the battery. Give a sharp tug on the leash, jarring the midget's feet loose from the ground, harvest the charged battery and replace it with a drained one from your utility belt.


    Shoot a hollow rubber ball attached to a thin hose under the leading edge of the rolling ball and harvest the resulting compressed air.
  14. Oct 19, 2013 #13


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    I think the OP needs to define "without touching it"? Can you use magnetic fields?

    If the moving object was a magnet and the gun contained a coil then as the object moved through the gun it's energy could be converted to electrical energy by the gun. Perhaps hard to make a gun with much range.
  15. Oct 19, 2013 #14
    Energy can only be transferred from one body to another by doing work on that system by some means.. So its not possible to transfer energy without work being done on that body.. In case of your theory of using guns is impossible to transfer energy i believe.
  16. Oct 19, 2013 #15
    Gravity does that, no?
  17. Oct 19, 2013 #16


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    No. Not in the way posited in this thread.
  18. Oct 19, 2013 #17
    how about you use released photons from laser cooling and use it on somekind of photo cell ? where it turns light energy into chemical energy , but anyway i dont think laser cooling would work on macroscopic objects
  19. Oct 19, 2013 #18
    there is also another way , you could make some sort of a gun like that batman uses to climb up buildings * no kidding *
    and then shoot it at the ball such that it sticks to the ball , and the length of the wire is exactly equal to the distance between you and the ball . after the hook reaches the ball , the gun somehow clings to the wire , such that for the ball to move it has to pull the wire , as it pulls the wire , the wire generates heat due to friction with the gun , you now have " sucked " the energy from the ball , its not 100% because some energy is lost due to friction between the ball and the ground , and also due to the fact that storing heat energy is always a pain in the *** and leads to a loss of energy " specially if the energy is not great enough to boil water for instance "
  20. Oct 19, 2013 #19


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    I mentioned laser cooling since 1) maybe the OP wasn't aware of that technology and it would be interesting to him/her and 2) to get the OP to be more specific - I did not mean it as an example of a way to harness any energy (only take away energy), I should probably have pointed that out more strongly :smile:.

    Anyway, these two things are central IMO:

    1. "touching" is a slippery word and it would be good if the OP defined what he meant (like CWatters said), and
    2. you can not transfer any energy to/from an object without interacting with it
    So it all depends on what kind of interactions the original poster would allow.
  21. Oct 20, 2013 #20


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    If you allow "intermediary" touching (which shooting projectiles would imply anyway) this setup would work:

    Let's say your ball (A) is rolling to the right. Put an obstacle (B) in the path of ball A. Put another ball (C) to the right of obstacle B, touching it. Put something like a toy dart gun (with a spring, like this) in position to collect ball C:

    ...(A).->...........|B|(C)....->.Dart gun

    When ball A hits the obstacle B, ball C will be put in motion to the right (and ball A would stop), due to conservation of momentum (like e.g. Newton's cradle). Let ball C roll into the dart gun, compressing the spring. Now you have energy stored in your gun, and your gun never touched ball A.

    Not very useful I presume :biggrin:, but it is a solution to the problem (if the original poster allows it).
    Last edited: Oct 20, 2013
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