how can mass be converted into energy?

how can mass be converted into energy when the mass is already energy? I was reading about mass defect, and it says that the mass is converted into energy. How is that possible?

 

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Mass is not normally considered energy.

 

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Sometimes it's the simplest questions that have the most physics in them

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In this case, remember \(E=mc^2\).

Essentially what this equation says is that there is a certain amount of energy ``stored'' in matter. This is, for example, how nuclear reactions work. In, say, fission, a small amount of the mass of the parent neucleus is converted to energy---this results in a liberation of (LOTS) of energy, and can be used to build bombs, etc.

In that case, the ``energy'' is stored in the bonds of the protons and neutrons to each other.

 

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So energy is converted into binding energy, right? So we can still consider mass as energy.

 

You are right mass is energy, but when people say "convert mass into energy" they mean "convert the energy stored in the matter into heat or kinetic energy".

 

But in this way, we talk about mass defect, so it isn't converted into heat or kinetic energy, binding energy is not one of them, right?

 

http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

 

Atom bombs don't even convert mass into energy. They convert the nuclear mass defect, which is a different thing. Reactions involving antimatter convert mass into energy.

 

I think that yours is a very strange POV.

It is true that mass, for example, of U235 is only very slightly more than the total mass of the fission products, but that difference is mass converted into energy. The only way to justify what you state (I think, but if you have some other way, tell me) is to insist that only when 100% of the starting mass is converted into energy does the process deserves to be called "converting mass" into energy.

To illustrate how strange your POV is lets apply it to conversion of gasoline, instead of U235 etc. into heat, radiant and mechanical energy.

In accordance with your POV is it wrong to state that Internal Combustion Engines convert chemical energy into mechanical energy and heat because they do not convert all (100%) of it into mechanical energy and heat (some always escapes in the exhaust as either unreacted gasoline or only partially oxidized as for example CO - just as nuclear fission, in your POV, does not convert mass energy into heat and radiation energy because it does not convert all (100%) of the original mass energy.

Likewise even your "anti mater" usually fails to convert all of the available mass into energy if any electron/ positron pairs are produced OR if the normal mater and anti mater masses are not exactly the same. - For example when an anti proton that is annihilated in a diamond.

 

The nuclear mass defect is neither fish nor fowl. Very technically you could call it mass, but it's none of the elementary particles, it's more like "captured" energy. None of the particles of any of the atoms in the atomic bomb, as far as we know, is converted to energy.

 

fusion

 

That's not quite true.

One of Einsteins arguements is that there was no such thing as matter, but trapped forms of energy.... or trapped forms of light as we commonly go by now.

 

And can I ask you one very interesting question? If we have only one nuclei (lets say 1 neutron 1 proton), and if we separate it on half (1 neutron separated from 1 proton), will then the binding energy be converted into mass?

 

How are you planning on separating the two?

 

No, it is not a technicality. Mass is mass – mass is not an exclusive property of particles. Many forms of energy are mass, "make gravity" etc., but not all.

I invented a simple rule that seems to work about what types of energy are mass. It is:

"Any energy which is the same in all inertial frames is mass and like all mass makes gravity, but any energy which is frame dependent is not mass and makes no gravity."

{To make this judgment correctly, with math etc., you need to be well versed in general relativity or perhaps nuclear particle physics when the Higgs is confirmed., but I know of no error in my simple rule.}

For example, because of its Thermal Energy, TE, a hot piece of lead sitting on the lab table containing 6E23 atoms has more mass / energy than a cold piece of lead with 6E23 atoms even if the cold lead has recently been shot from a gun and in your lab reference frame has much more Kinetic Energy, KE, than thermal energy, TE. This follows from my rule because TE is the same in all inertial frames*, but KE is frame dependent (KE = 0 in the bullet's frame, etc.) The hot lead mass also generates more gravity than the cold lead 6E23 atoms can.

Likewise there is no gravity between two photons traveling along side each other as their energy is frame dependant (red and blue shifts etc.) and they have 0 rest mass. If there were attraction between photons, I suspect the distant stars seen with your right eye could not be seen with your left eye because the essentially parallel traveling bosons would coalesce into very fine filaments when traveling for light years, distance D away, with such a small divergence angle < ~0.5d/D in radians, on average, where d is the stellar diameter. Last time I looked, both eyes saw the same stellar pattern in the heavens.

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SUMMARY: there is no reason to treat any of the following forms of mass/energy different from any of the others: The binding energy, both chemical and the nuclear the mass defect, the thermal energy, the chemical energy in octane that can be released by oxidation (which is less than the total energy or heat of formation in binding), the energy in a spinning gyroscope, etc.

As I said before, your singling out the nuclear mass defect for special treatment as some unique sort of mass energy or only “technically correct” to be considered as “mass/energy” is a very strange POV – Reflecting a lack of adequate understanding, I think.
At least it is not "total nonsense" as sometimes you post. You are interesting as at other times you have a good understanding of things - I am only trying to help make that the normal case. Please take no offense.
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*If this were not true, then one could not state one melting temperature of lead etc. Instead one could say things like on Jan 1 2008 lead metlted at T1108 on 1February 2000 lead melted at T1208 etc as the Earth is changing frames as it goes around the sun.

 

No. It already is mass when they were bound. Some other source of energy probably has lost mass to make the separation, if you go back to the origins of that energy. - It gets complex. For example if the immediate cause of the splitting is the collision with a energetic neutron then the three particle system will have the same total energy after the collision as it had before so the system defined by these three particles will still, I think but not 100% sure, have the same mass/ energy as before but the "bigger system" which includes the generator of the energetic neutron may not have its mass/energy conserved. (For example, something with kinetic energy may have a change in the KE but KE is not mass / energy.) See my post replying to MetaKron.

I hope Bentheman]/b] is reading and corrects any errors I have made (here or in that post). – He was properly more cautious and asked first how were you going to make the split.

 

Not strange at all to think of matter as that which consists of actual particles, Billy. "Mass" is a pretty slippery term.

The fact is that we don't have a way to convert atomic matter into energy except by reaction with antimatter. You still get the same number of the classic particles like electrons, protons, and neutrons. The energy that is released in a classic nuclear reaction is like extra baggage.

 

There needs to be a conservation in energy. I might be wrong, but if you could seperate a proton and a neutron, the binding energy would return to the source, the quarks that constitute the neutron and the proton. You see, when quarks come together, one paradoxical situation is that they contain more energy than what they had originally. The surperfluous energy is then converted into gluon material. I would then imagine, if you reversed the process, the quarks would regain some of that energy. I don't see any reason for the gluon energy to become mass, unless the conversion is invariant under such processes.

 

Hello all

The mass of a proton is more than the sum of three individual quarks. So there is more to mass than just particles.

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When I have 50 pounds of fat on my tummy and I walk allot and stop eating for a few weeks or so , it is converted to energy and seems to dissapear!

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