Kinetic Energy

Discussion in 'Physics & Math' started by jordak6200, Sep 13, 2006.

  1. jordak6200 Registered Member

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    If an object is alone in the universe, can it have any kinetic energy?
     
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  3. Mosheh Thezion Registered Senior Member

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    YES... but it could never be converted into anything else.
    unless there is some unknown minor level of drag from spce itself.?

    -MT
     
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  5. Dinosaur Rational Skeptic Valued Senior Member

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    If an object is alone in the universe, what does it mean for it to move?

    I do not think it can have kinetic energy, becuae it seems difficult to define motion relative to nothing else.
     
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  7. Pete It's not rocket surgery Registered Senior Member

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    I think if it's alone in the universe, its motion can be anything you want it to be.
    So it can have KE, but its KE can have any value at all... that makes the notino of KE in that context useless or even meaningless.

    It's a bit like this:
    Consider a 2D world, with an x-axis and a y-axis.
    Does that world have a z-axis position?
    Clearly it does, if we choose to define a z-axis origin in a 3D-space that includes the 2D world.
    But if the 2D world is the only known context, then the z-axis position isn't useful, and perhaps not even meaningful.


    It's also a bit like the colour of an object in the dark... it will be some colour when light, but while it's in the dark, the notion of its colour isn't terribly meaningful.

    "What colour is an orange in the dark?" was a long standing, perhaps unresolved question on SSSF (a forum I used to haunt).
     
    Last edited: Sep 14, 2006
  8. geistkiesel Valued Senior Member

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    If the object moves it has kinetic energy according to current dogmatic understanding.

    Geistkiesel
     
  9. funkstar ratsknuf Valued Senior Member

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    Good question!

    It relates closely to Mach's Principle, which basicly states that motion must be relative to something. In an otherwise empty universe, there's nothing to relate to, and motion is meaningless. The other viewpoint is that even with nothing in it, the universe has an underlying structure that is absolute, and relative to this, concepts such as kinetic energy make sense. There's a famous argument called Newton's Bucket which discusses this. In a Machian universe, there's no bodies to relate a rotating bucket to, so the water surface would remain flat regardless of it's "motion". In a Newtonian universe, even with no other bodies to relate to, the bucket can be seen to be rotating if it's water surface is curved.

    This Wikipedia article seems to give an overview of the different philosophies regarding this. I can recommend Brian Greene's The Fabric of the Cosmos if you want a nice introduction to modern cosmological thinking, and how we got there. It's very well written.
     
  10. jordak6200 Registered Member

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    I must say I came to the forum hoping to find one definite answer, but there is none, is there? I suppose this is more of a phylisophical question than a scientific one.
     
  11. JetPilot Registered Senior Member

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    It sounds like philosophy, but it is science - thoughts, suggestions, answers to questions in science actually need more validity than philosophhy itself.
     
  12. CANGAS Registered Senior Member

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    If the entire mass of the universe is alone in the universe, can it have kinetic energy?
     
  13. JetPilot Registered Senior Member

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    And I dont understand why kinetic energy is so unbelievable. How about you ask yourself: Why should objects in motion come to a stop? Nothing should make them stop - that makes even less sense if you really think about it.

    As for CANGAS, why wouldn't it? I doubt its kinetic energy or the lack of it thats the issue - it is rather the fact that there is no external reference able to witness it in motion.
     
  14. CANGAS Registered Senior Member

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    1,612
    Kinetic energy has an exact and specific definition in relation to the accomplishment of work. Work involves one body doing the work and one body being moved so as to fit the definition.

    If the only inhabitant of the universe were one particle, there would be no other thing which could be acted upon to accomplish work.

    In a similar idea, if the entire mass of the universe were considered to be the body wanting to do work, upon what could it act to do work?
     

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