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Mass and energy

  1. Jun 19, 2004 #1
    can mass changed to energy
    and can energy changed to mass ?
    if no why ?
  2. jcsd
  3. Jun 19, 2004 #2


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    Yes, both are possible.

    - Warren
  4. Jun 19, 2004 #3
    i don't understand this. i know they are two words for the same thing but i don't know how. i know fusion or fission (one of them) converts mass to energy, so would the other convert energy to mass?
  5. Jun 19, 2004 #4


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    Matter-antimatter reactions are the classic examples of the interconvertibility of mass and energy. If you slam a proton and an anti-proton together, you get gamma rays -- mass has been converted to radiation, which is massless but energetic. Conversely, if you put enough radiation in a small enough area, you'll provoke the creation of a pair of particles, one normal matter and one anti-matter -- energy has been converted into mass.

    Nuclear reactions are another common way to see the equivalence. When energy is realeased by a nuclear reaction, you can be assured that the products have less total mass than the reactants.

    - Warren
  6. Jun 20, 2004 #5
    cool. i still don't understand the actual physics of it but ill try to find out.
  7. Jun 22, 2004 #6
  8. Jun 22, 2004 #7


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    Fusion and fission both convert matter to energy- that's why both are used for bombs! A tiny amount of matter converts to a huge amount of energy.

    Conversely, a huge amount of energy converts to a tiny amount of matter. Currently the only observable examples of energy converting to matter are elementary particles.
  9. Jun 24, 2004 #8
    a huge amount of energy = a huge amount of photons(Δm)
    a tiny amount of matter = imply energy(m0)
  10. Jun 25, 2004 #9
    I think it is incorrect to say that mass is converted to energy. Mass IS a form of energy. What happens in a fission process is that the mass energy is converted to kinetic energy.

    Or maybe this is just a matter of semantics.
  11. Jun 25, 2004 #10
    "Mass converted to energy" or "Mass energy converted to kinetic energy" is just a terminology problem. Whatever the case, mass is equivalent to energy, and we don't need to argue more about that.
    A huge amount of energy is needed to produce a small amount of mass, as said in Einstein's famous equation:
    E = m c2
    Since c, the speed of light in vacuum, is a pretty big number(299792458 m/s), that's quite a lot of energy for a small amount of mass.
  12. Jun 25, 2004 #11


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    Since this is a physics forum, I feel compelled to nitpick and add that the formula you mentioned is incomplete. There are higher terms that have been left out and that incorporate such things as kinetic energy for example.
  13. Jun 26, 2004 #12
    I would argue that surely mass and energy must both be part of the same thing - not different versions of the same "mass-energy". ( ie - Energy HAS mass, not that energy can be converted into mass and vice versa.)
    I've come up with a simple arguement for this - imagine a football; you kick this ball converting chemical in yours muscles to kinetic energy. Hence the all moves and gets heavier since it has gained mass - the energy it gains is the SAME as the chemical energy i have lost because energy has been conserved. Now, if energy and mass were different versions of the same thing, then surely 2 things would happen instead - 1) the ball would move (since gained the energy from my chemical) but would not get heavier, because all energy has gone to energy and not mass, as it can be proved that the ball gains the same energy as I have lost, or 2) the ball would not move, just get heavier as energy goes to mass. Both are untrue - therefore energy must HAVE mass, rather than BE mass.
    From this we could also conclude that photons have mass, which in a way would make sense if you think about it - after all light can not escape the gravitational field of a black hole. Therefore is must have weight. Therefore it must have mass.
    What do you think? :-)
  14. Jun 26, 2004 #13


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    Do not post personal theories here. Personal theories are welcome only in the Theory Development portion of the site.

    - Warren
  15. Jun 27, 2004 #14
    May I ask why?
  16. Jun 27, 2004 #15
    If there is a problem with what I said, then please just remove it. Thanks. :-)
  17. Jun 27, 2004 #16
    Because if it is wrong, and people unfamiliar with the forums take it as a proven theory, then it could get confusing. Whereas if it is in the theory development section, then that is well stated. Also, i am no expert physicist, but what you have said is based on a very common misunderstanding. The things in 'our' world behave a lot different to those in the quantum world ie. Spin, a component of quantum particles, is undefinable by anything that we understand in 'our' world. Thus it is probably very likely that what you have stated, does not hold up in the quantum world of elemntary particles. And could you verify why you believe photons entering a black hole, and not leaving, must have weight, and therefore mass. Because the equation for weight is: Gravitational field strength x mass = weight

    Now no matter what the gravitational field strength is, if mass is 0, then weight will be 0. Relatively, if the weight is 0 then the mass is 0. Photons dont need to have weight to be unable to escape a black holes gravitational pull. It is the curving of space, which everything 'follows', that causes the gravitational effect. It is not mass that causes gravity. Therefore i cannot understand how you came to the conclusion that photons have weight.

    Last edited: Jun 27, 2004
  18. Jun 27, 2004 #17
    That was not the main point of my arguement - if you read the rest then it does appear to make sense. Also, it is a known fact that photons have momentum - it is what the De Broglie Quantum Wavelength equations are based upon. Hence, if a photon lacks mass then how can it have momentum if momentum = mass * velocity? My football arguement does, to some extent, appear to make sense and would coincide with E = mc2.
  19. Jun 27, 2004 #18
    Does anyone at least consider it valid and reasonable? :-)
  20. Jun 27, 2004 #19


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    This is your second, and last warning, Cheman. Stop posting personal theories.

    - Warren
  21. Jun 27, 2004 #20
    I apologise if what I have said has not been posted in the correct way or place - i do not mean to cause confusion, simply ask questions, which is surely the whole idea of science. However, I would just like to ask (if you would like to tell me by perosnal email as not to cause further confusion) what you thought of my idea?
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