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Where is kenetic energy stored (potential energy)

  1. Apr 22, 2012 #1
    Ok so a friend and I were talking and a question came up about where is the kinetic energy of an object stored? You see the whole idea is around the fact that kinetic energy is information right? So we thought of a thought experiment for this, lol. Let's say you are in a ship in space, there is nothing in this space, no stars planets or anything not even vacuum fluctuations to try and tell how fast you are moving. Also the ship is not accelerating or decelerating. Also the speed is anything you want it to be as long relativistic effects don't matter, So how would you tell how fast you are moving? If the kinetic energy is information and it is part of the ship then how would you use it to tell how fast you are going? Also I know that in different frames of reference, the ship's kinetic energy could be zero and thus it is stored nowhere and at least from that frame, it is correct but I am talking about the fact that it is moving and obviously has energy, if there was an object in front of the ship and at some point in the next year it will hit it, there is going to energy released in that impact because of the ships speed (kinetic energy). Also this ship has no windows, lol

    I am pretty sure it is stored in the object itself, now I don't know where or even how it is stored on it though.

    My friend thinks it has to do with the mass increase from relativity, basically since no matter how fast you are moving there is always some amount or mass increase even at 1 mph there is a extremely small amount. So by doing experiments inside the ship with a particle accelerator, you could figure out how fast you must be moving. You would just have to do them in every direction to figure it out since in one direction the particle would never go faster the light and it would seem to go slower than the other directions, nevermind i just had a thought, even this wouldn't work, because from the observers (you) point of view the particle would go the speed of light in every direction, even in the direction of travel, even if the shipp was moving at 99.9999999999 and the particle was as well. from a outside observer, the particle would never go faster then light though.

    So where is the kinetic energy of the ship stored and how is it stored and how in the scenario would you find out how fast you are moving since the ship has a certain amount of kinetic energy, and if that is information then there should be away to read it.
    Last edited: Apr 22, 2012
  2. jcsd
  3. Apr 22, 2012 #2
    So does anyone really have an idea of where the kenetic energy is stored? I am pretty sure it is stored with the ship but how is it stored with the ship?
  4. Apr 22, 2012 #3


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    Kinetic energy is not related to information. In addition, kinetic energy is not a property of an object, but a property of an object in a specific frame of an observer. Kinetic energy (and velocity) depend on the frame of the observer.

    There is no absolute velocity. Relative to the ship, the ship is always at rest. Relative to observers moving relative to the ship, the ship is moving (not really unexpected...).

    Moving relative to what?
    If there is an object which moves relative to the ship, the ship has kinetic energy in the frame of this object.

    This exists only in reference frames where the ship is moving. And usually, it is not called mass (which is reserved for the mass at rest), but energy.

    No, this would violate relativity.
  5. Apr 22, 2012 #4
    Ok so the kinetic energy of the ship isn't really information at all if there are no observers with a different reference frame. Is this correct.

    Well you said
    Where is that energy stored, since it is moving, relative to the stationary object.
    It has energy, more so than if it was stationary as well, so when it collides with the object, no matter what view you take it is still moving and is going to hit that object with however much energy it would have at that speed. Even if I was in a ship next to it and from my point of view it has no kinetic energy, it still has energy, because at some point it will hit that stationary object?

    I am thinking it might be easier to explain in our universe like ours and not this thought experiment universe, lol
  6. Apr 22, 2012 #5


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    Well, you can always imagine observers with arbitrary speed (<c) in arbitrary directions and calculate how the system looks to them. It does not matter whether there is actually an object which could "observe" things via a camera or similar devices.

    In every particle which is moving. It has a higher energy just because it is moving.

    ... in a different frame. As you can see, you cannot say "an object has kinetic energy". This is wrong. But you can say "an object has kinetic energy in this frame".
  7. Apr 22, 2012 #6
    Kinetic energy is not stored anywhere, it is a relationship between the an object and an observer and is dependent on their relative motion.
  8. Apr 22, 2012 #7
    Ok now it kinda makes sense, i need to think about more, lol I might have another question later though, lol
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