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What Exactly Is Energy?

  1. Jun 26, 2004 #1
    I know this question may sound a bit basic, but it is actually quite interesting. We know the two forms of energy are potential energy and kinetic energy, and that these forms of energy can be in many forms (e.g. thermal energy, elastic potential energy, gravitational potential energy...). However, what I don't really understand is, how is this energy actually stored? By this I mean, for example, how is kinetic and potential energy stored in terms of particles. Has it got to do with the amount of vibration or the separation between the particles? Also, if matter is equivalent to energy is matter therefore a form of energy? I'm sorry if it sounds confusing but I just find energy a really hard concept to visualise, it's not something easy to visualise such as matter. I would appreciate any help given.
  2. jcsd
  3. Jun 26, 2004 #2
    If you don't wish to visualize it, you don't have to. I prefer to think of energy as a bookkeeping concept. No one has seen energy, or felt it, etc. In fact, you might even say we concocted the concept in such a way that it always appears conserved. For example, when matter disappears in a reaction and kinetic energy is gained by the surrounding particles, we notice the relationship between mass and released energy and set m = E/c2 so that it appears energy only changes form. However, it provides such a conveniant analogy that one would be hardpressed to overlook it. By using concepts of energy we can avoid manipulating the time variable and therefore skirt issues in problems that would otherwise require being dealt with more upfront. Also, one look at a potential function graph can almost immediatly give an idea of the motion of a body.
  4. Jun 26, 2004 #3
    you feel energy and see it in every day life , the movement of the winds , lightning, etc
    thats my only quam with wat you said suffian
  5. Jun 26, 2004 #4


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    I agree completely with suffian. The history of "energy" has been that we keep adding new kinds of energy in order to maintain "conservation of energy"! Including, with the advent of relativity, considering mass as a kind of energy!
  6. Jun 28, 2004 #5
    The unique energy existing in the universe is energy of light. It as the speed of light absolute too. All other speeds and energy are relative. They are consequence of properties of light. It is not casual that value of speed of light is present at the mass- energy relation.

  7. Jun 28, 2004 #6
    Actually that c comes from Permittivity and permeability of free space... electromagnetism stuff. It is also not casual that e is every where as well. If anything you're describing things in a very mathematical sense.
  8. Jun 28, 2004 #7


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    Agreed. To follow up on your argument, you could replace c with [tex]/epsilon[/tex] and [tex]/mu[{tex], et voila: you have those two popping up in every other equation.
    "The energy of light" sounds almost philosophical.
  9. Jun 28, 2004 #8
    “The energy of light” looks not philosophically when the beam of laser burns metal, for example.
  10. Jun 28, 2004 #9
    When traveling at c, does mass gain or loose energy?

    Theoretically speaking of course.
  11. Jun 28, 2004 #10
    Mass can't travel at c. This is privilege of light only.
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