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E=mc^2 (general physics?)

  1. Jun 11, 2012 #1

    Energy is mass times lightspeed squared.

    Outside our earth spere there is zero gravity.

    Why wouldn't gravity determine lightspeed to be between 1 and 2 squared "c"?

    Is there a single variable for distance between the planets?

    This is induction, not sure what it means and what not.

    Is it only 'space' or something to 'overcome' between sun and earth?
  2. jcsd
  3. Jun 11, 2012 #2

    Vanadium 50

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    I'm sorry, but virtually none of that makes any sense, and what does is not correct.
  4. Jun 11, 2012 #3
    c is a constant so no. The rest of relativity is derived assuming that this is constant.

    I'm confused about your thought process. Are you assuming that since the gravitational potential energy changes, that [itex]mc^2[/itex] should change? If that is the case, you are well out of the applicability of [itex]E=mc^2[/itex] which is only the energy of an object that is at rest.
  5. Jun 11, 2012 #4
    I'm not sure.

    I have no physics.

    I feel (not more), that c is constant but c squared, that is why I'm not certain.
  6. Jun 11, 2012 #5


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    As you can probably tell from the other posts, we're all just trying to get a handle on exactly what it is you're trying to ask. Toward that goal, I will ask several questions:

    It appears you are following a single chain of cause and effect here, but I don't quite see it. If you could explain in a little more detail why and how you think gravity would determine lightspeed to be between 1 and 2 squared c, the question would be a bit more clear. It should also be pointed out that the definition of c is "the speed of light," so lightspeed cannot be any faster than c (nor any slower, for that matter).

    Sure; d, if we define d as "the distance between planets" (JK). But seriously, since you were just talking about gravity, I'm geussing that you're looking for some kind of limits (imposed by gravity) on how close the planets can be to one another. Is that right?

    Are you inferring a connection between lightspeed, gravity, and ellectrical induction, or are you saying this is your induction into this subject? Also, what exactly is the subject here? Are you trying to get a better understanding of orbital mechanics? Lightspeed (special relativity)? Gravity (general relativity)?

    Maybe this question will become clearer if you can fill us in on the other stuff I asked.
  7. Jun 11, 2012 #6
    So mass plus lightspeed squared' is about energy.
    Is there more to say about energy from the same equation?
    My original inspiration. Outside and nearby earth in zero gravity space. What about the object on earth and outside it. I want to reason about the object intself in different areas.

    Yes, you're right.

    Orbital mechanics and a better understanding of it.
  8. Jun 11, 2012 #7
    Ultimately I came to not understand if there is differences in space in comparison to on a planet. I do understand this now (I do not actively think so much), so energy seems be equivalent everywhere but things need more velocity on a planet,

    however, does this mean particles and only with 'gravity'' there is entropy?

    Is there a constant for entropy? That would answer my question if positive. Namely all energy of objects(') equal? (chemistry)

    I get back and thought: what formula? If there is a way to reason about a single object, is entropy all the same 'relatively'?
  9. Jun 11, 2012 #8


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    First it may help to understand exactly what energy means in physics. Basically it means "The ability to perform work". If you pick up a book, you have performed work on that book, which means it required energy to pick it up. So the phrase "energy seems to be equivalent everywhere" doesn't really make sense, as we just use it as a measure of the ability for something to do work. Unless you are saying that one joule here on Earth performs the same amount of work as 1 joule does in space, which is true.

    Also, two objects with identical masses will require the same amount of energy to accelerate to the same speeds, irregardless of where they are located at. (Ignoring losses such as friction of course)

    I don't really know what you are asking. Entropy is a concept related to energy. It is usually stated as the amount of energy not available for work in a thermodynamic process. So in a perfect situation you would expend X amount of energy and perform Y amount of work. But unfortunately the universe doesn't allow "perfect" devices and you will lose energy in the process due to heat loss, friction, and other ways. So X energy gets you LESS than Y work.
    The full equation is actually E2= M2C4+P2C2
    where P is the momentum of an object. The short version of the equation without the momentum times c squared is only applicable if you want to talk about the energy of a non-moving object.

    Also, there is most assuredly gravity in space. Gravity is what attracts the Moon to the Earth, the Earth to the Sun, etc. (Also the Earth is attracted to the Moon, the Sun is attracted to the Earth, etc) Zero gravity is a misnomer. When you are in space you are effectively in "free fall", which causes you to have no WEIGHT. So you would be weightless.
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