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E=mc^2 for ordinary matter?

  1. Dec 27, 2005 #1
    I saw in a TV show about E=mc^2 by NOVA that a physcist said that it was possible to convert the mass of for example, an ordinary pen into lots of energy through E=mc^2

    I know how energy can be unlocked from Uranium atom but how could one unlock the energy from an ordinary pen?
    Would it take more energy to make this transformation than the total energy got out?
    Last edited: Dec 27, 2005
  2. jcsd
  3. Dec 27, 2005 #2
    If you had an equal number of anti-electrons and anti-protons etc. as the pen, and put them in the same points in space-time, you would have radiation. The energy of this radiation, [itex]E[/itex], and the mass of the pens [itex]m_0[/itex], would be related by


    since we have 2 pens.
  4. Dec 27, 2005 #3
    But anti-pens aren't exactly available in stationery shops...
    Can we make antimatter in an accelerator without making matter as well?
  5. Dec 27, 2005 #4
    E=m*c^2 is just a relationship between mass and energy, and not telling how to convert them. So shouldn't we assume it implies a condition, "if we can convert mass to energy (either technically or theoretically)" and vice versa? It's another problem, I think.
    Last edited: Dec 27, 2005
  6. Dec 29, 2005 #5


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    Adding and clarifing from maverick, E=mc2 is simply an equation stating how much energy there is in the pen.
  7. Dec 29, 2005 #6
    Well if we had the ability to annihalate the mass of a pen and convert it into energy you'd have one powerful bomb (probably power generation would be out of the question as it would take more energy to create the antipen then you would release in the subsequent annihalation)

    As to your second question, we can create antimatter, but only in very small quantities. If I remember correctly one of the key problems in building the positron collider at CERN was finding a way of creating and storing the positrons until they were needed in the accelerator.
  8. Dec 29, 2005 #7


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    The person on television was speaking theoretically- that much energy is in the pen- there is no currently feasible way of getting it out.
  9. Dec 29, 2005 #8


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    While you won't get anything like full conversion, you can simply burn the pen. The small amount of matter that is actually converted to energy will follow the formula.
  10. Dec 29, 2005 #9
    Just read about that today.
    Even in chemical reactions, mass is not conserved. But it's so small amounts that it can be neglected. In chemical reactions, i.e. outer shell electron physics, it's about eV. Whereas for example in nuclear physics we deal with MeV. So (delta)m=(delta)E/ c^2 must be taken into account.

    So E=mc^2 always applies, even when I lift the pen some tiny mass is converted into energy in my muscles.
  11. Dec 29, 2005 #10
    I don't think that is true. When you lift the pen, you do work equal to Force*distance. The total work would be (mass of pen)*(gravitational constant on earth)*(distance you have lifted). That work or energy is provided by you.

    So lifting a pen has nothing to do with E=mc^2.
  12. Dec 29, 2005 #11
    He said in his muscles.
  13. Dec 29, 2005 #12
    I interpreted this as his muscles (which in turn means his body) providing the work or energy needed to lift the pen. But this energy does not have anything to do with the loss of mass of the pen through E=mc^2.
  14. Dec 30, 2005 #13
    Of course not. All he was saying is that some mass in the body was converted into energy so that muscles can do work. For example, some mass from foods we eat is converted into energy.
  15. Dec 30, 2005 #14
    I have completely misunderstood. That is an interesting point of view. But is the energy we use in our daily life predominately come from the conversion of mass into energy through E=mc^2? Since we are biological beings, I'd have thought there would be a much more complicated and hence inefficient way to produce energy.
  16. Dec 30, 2005 #15


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    Where did you read that? I thought that in chemical reactions, the outer shell electrons transferred from one atom to another but certainly were not annihilated. I was under the impression that mass to energy conversions only occured in nuclear reactions.
  17. Dec 30, 2005 #16

    Doc Al

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    Ratzinger's source is correct. E=mc^2 applies everywhere, not just in nuclear reactions. Of course, in chemical reactions no particles are annihilated, but (for exothermic reactions) chemical binding energy is converted to thermal energy. This gets reflected in a decrease in the total rest mass of the constituent particles. For chemical reactions the change in mass is ludicrously small.
  18. Dec 30, 2005 #17
    I don't quite understand the statement. Since only the chemical binding is converted to thermal energy, why would the mass of the constituent particles decrease? Chemical binding don't have mass, isn't it?:confused:
  19. Dec 30, 2005 #18

    Doc Al

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    All binding energy, chemical or nuclear, has an associated mass. The difference in mass before and after a reaction is proportional to the energy released. Of course, since nuclear forces between nuclei are much stronger than the electomagnetic forces between molecules, nuclear binding energy is much greater than chemical binding energy.
  20. Dec 31, 2005 #19
    Besides binding energy, are there any other form of energy which have mass too?
  21. Dec 31, 2005 #20
    Unlocking energy from Uranium atom is part of the radiactive fission process which leads to emission of energy whihc is basically the "lost" mass , for exampe , if you can take an atom and split it into two , you will get two pieces whose sum of masses would be less than the intial total mass of atom ... the lost mass is emitted as energy.

    What is meant by [tex]E=mc^2,[/tex] is that mass is basically a condensed form of energy and both these are interconvertible. , destroying "m" mass in space would leat to emission of radiation with E given by above expression , and is applicable to all matter.

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