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Any energy generation process means mass loss?

  1. Feb 20, 2013 #1
    Hello all,
    Considering that Einstein told us that E=mc2, that means that any energy is generated at a cost of mass loss?

    to be more specific:
    When a power plant generates energy by burning gas or coal, a part of the particles in the fuel burned simply disappear and can't be found in the gases generated by the burning process?
    When a wind turbine generates electric energy, is there any mass loss? (particles transformed in energy - from the air that pushes the wind blades maybe or from something else)
    When a light bulb generates light and (thermal) energy - are there some particles converted into photons and heat?

    matter is not conserved because some of the mass of the fusing nuclei is converted to photons
    my question is: which parts of the fusing nuclei are converted to photons? The neutrons? the protons? Are there elementary particle that can't be converted into photons in the nuclear fusion process?

    Last edited: Feb 20, 2013
  2. jcsd
  3. Feb 20, 2013 #2
    If I understand you right, yes.

    Weigh a spring. Compress it. Now it will weigh more, from the extra energy. This is different from nuclear decay type stuff because no mass is turned into energy. Rather, the mass has energy added too it which increases its weight. Once the spring uncompressed its back to its old weight (ideally). In a nuclear processes some of the actual particles change or disapper resulting in their energy equivalent being released.

    edit - Check out the full version of that formula you wrote. The one with a 'p' in it. Google it if you don't know. That full equation has a 'p' which is momentum, which is related to kinetic energy. This might make it more understandable. If you have something moving it has momentum (and kinetic energy) and the equation you wrote doesn't work. What you wrote is a simplification for an object at rest.
    Last edited: Feb 20, 2013
  4. Feb 20, 2013 #3
    Thanks but I think your example is not relevant for my question, since the spring is 'storing' the energy and it will release it later. But when a power plant is generating energy, that energy will be consumed by consumer electrical devices.
  5. Feb 20, 2013 #4
    If the energy is stored, not necessarily in a spring but perhaps a chemical battery, or as gravitational potential by lifting something up, then the associated gravitational force goes up along with it, because of the added energy. Energy your device doesn't store goes off becomes part of other systems of stuff, affecting them the same way.

    At the power plant side the fuel should weigh less after being spent. How much less is proportional to the amount of energy it lost.
  6. Feb 20, 2013 #5
    Ok, I found the formula E2=m2c4 + p2c2
    So when the wind blades move, the momentum (p) is transformed into a flow of electrons; therefore the generated energy doesn't imply any mass loss. The flow of air is transformed into a flow of electrons. (or at least that's what I understood).

    However, when the flow of electrons (electricity) reaches a light bulb generating heat and light, how are the photons generated? Are the electrons transformed into photons?
    Last edited: Feb 20, 2013
  7. Feb 20, 2013 #6
    I used the term "lost" with the meaning of "disappearing as material particle", like "transformed into energy". I didn't mean "lost" from the point of view of it's human use.

    No energy is lost since it will go somewhere, regardless of it being used by anyone.

    So my question was:
    In a power plant, some of the particles in the fuel are converted into energy (disappear as particles) instead of becoming part of the waste gas (CO2, CO, etc)?
  8. Feb 20, 2013 #7


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    Staff: Mentor

    Nope. All the particles are still there. They are just rearranged into different configurations. This rearrangement ends up releasing binding energy which is used to run the power plant.
  9. Feb 20, 2013 #8
    I understand. But in this case why the binding energy is not present in the formula "E2=m2c4 + p2c2"?
    Because the energy the fuel based power plant is generating is not produced by any particles transformend into energy (m) nor by the impulse of any movement (p).

    I guess the binding energy is the energy stored by in the bonds between C, O and H in the fuel. Can you give me some information or links about the nature of the binding energy?
  10. Feb 20, 2013 #9


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    Staff: Mentor

    You misunderstand the equation. It says absolutely nothing about the source of the energy. It could be kinetic, thermal, radiation, etc. The equation simply allows you to find out how much energy an object has based on its mass and momentum, or how much mass an amount of energy has. It doesn't care whether that energy came from nuclear fusion, chemical reactions, heat, etc.

    A general definition is that it is the energy needed to disassemble an whole object into separate parts. This could be something as big as a planet or star, or as small as an atom or atomic nucleus. The only difference would be which forces you are working against.


    The key thing to understand is that during a chemical reaction the molecules end up in a state which has LESS mass/energy than they did before. This missing mass/energy is usually in the form of heat, which is transferred somewhere else and used to do work on something else, such as turn an engine.
  11. Feb 20, 2013 #10
    Nice answers, thanks.

    I have a further question though:
    I think the formula does say where the energy comes from, but considering only mass and impulse as a source, ignoring the chemical bond. All the other sources seem to be from "m" or "p".

    Is there any better formula that can explain the energy of an object considering all sources of energy? I guess that primary sources of energy are only a few anyways

    fusion/fision energy is explained by "m";
    heat is explained by "p" (movement of atoms);
    kinetic (movement of objects): "p";
    nuclear-generated radiation: "m";
    radio waves: movement ("p") of electrons (electricity) transformed into electromagnetic radiation: "p"

    It looks to me that there is only chemical bond energy left.
  12. Feb 21, 2013 #11


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    Staff: Mentor

    Really? Where in the formula does it take into account all 4 fundamental forces, the way they interact, the various masses of particles, and the distribution of other objects within space? After all, that is what decides how much energy something has. (Well, part of it at least) The formula is strictly a way to convert units of energy to mass and momentum or vice versa. It is nothing more.

    One formula? Nope. You're talking about all of the basic laws of physics, including Relativity and Quantum Theories, which aren't even united at the moment. Besides, if you are looking to formulas to explain nature, then you are ignoring the bigger picture, the theory itself. The theory is what explains things. The theory is what uses formulas and equations and whatever else to explain observations about nature. As such the theory of Special Relativity, which is where that equation comes from, says absolutely nothing about where the energy comes from. It doesn't care one bit! It only says that if an object has X mass and Y momentum then it has E energy.

    Potential energy explains it. The atoms had potential energy before bonding, and they gave it up afterwards. It is important to understand what binding energy is. If you have to use energy to take something apart, such as a planet or an atom, then when it goes back together it gives off energy and forms a bond. Because it gave off energy it is now in a lower energy state and has less mass.
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