# losing potential energy?

#### FredM

Joined Dec 27, 2005
124
The 1st law of thermodynamics “that energy can not be created or destroyed, it can only be changed from one form to another” is the question here.. If I have matter, and was able to convert this matter into energy @ E=mc2, what happens to potential energy 'held' by the matter?

springs.pdf attached shows the idea.. I have a container with a spring in it, in one case the spring is held in a stretched state (energy has been used to stretch the spring, some energy has been converter to heat in the process of stretching the spring, but now the spring is trapped in a stretched state, and has potential energy which can do work and therebye be converted to energy in some other form [recovered]).. I also have shown this spring in an unstretched state in the same containment.. This spring has no (elastic) potential energy.

If I convert both the containment and the spring to energy using E=mc2,
I cannot see how more energy would be produced from the stretched version than from the unstretched version (I have included the container so that no errors could result from energy imparted by sudden [!] removal of the spring).

If energy recovered is the same in both cases, then what has happened to the potential energy 'held' by the stretched spring..?

If energy is not the same in both cases, please explain how this can be.. I have been tortured by this problem (and many other variants involving other potential energy types) for days.. If I am being stupid, Please show me (simply) why, as I am obviously as thick as 2 short planks!

As I see it, the only way to get a different energy from E=mc2 would be to change m, as c is a constant.. therefore, in order to recover the potential energy held by a stretched spring, m for the spring+enclosure must be greater when the spring is stretched than when the spring is at rest.. this does not seem right to me!

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#### beenthere

Joined Apr 20, 2004
15,819
That potential energy may get lost in the decimals. Consider a 1 kg spring, stretched enough to have 1 joule of potential energy stored in it. Converting the spring's mass to energy gives us 8.8988 X 10^16 joules of energy. It's simply going to be very hard to see if that 1 joule of potential energy showed up. I suspect it may be there, as a slight increase in the light frequency (potential to kinetic).

#### recca02

Joined Apr 2, 2007
1,214
it might be responsible for some energy changes that might of the order of 10^-6 of the energy by mass. not only is this the case with a stretched spring but also at atomic levels where some potential energy is associated with every electron.

#### FredM

Joined Dec 27, 2005
124
It's simply going to be very hard to see if that 1 joule of potential energy showed up.
I agree that the contribution of any potential energy would be insignificant and unmeasurable with this method.. But the core question remains - by what possible mechanism could the potential energy be recovered? Is it only mass which influences E, or does something else vary?

ok - I am really unsure about the next - but.. If, instead of using E=mc^2, one made potential energy unrecoverable by some other method (without this energy being allowed to do work) what would be the outcome? I expect the following will get 'shot down' for good scientific reason, but here goes..

Let us take the containers (with spring in stretched and in unstretched states) and pour into these containers a compound which hardens with exactly the same mechanical properties as the springs.. One now has a solid block of uniform density containing the spring.(s)

If the block is then ground to powder, energy will be expended in the grinding process, but this energy should be equal whether the spring inside this block is stretched or at rest..

The potential energy from the stretched spring is lost (?) Energy required to render the spring (and encasing material) 'inactive' is the same for both stretched and unstretched versions (?)

I think the E=mc^2 route is far more elegant and less error prone - but is a bit difficult (!) to test !!

Other experiments could include magnets arranged as per the spring, and gravitational potential energy, and others.. What would happen, for example, to the potential energy 'held' by Voyager's mass if (now that it is in interstellar space) it was zapped by a Vogon battle cruiser and converted to energy at mc^2 ?

#### bloguetronica

Joined Apr 27, 2007
1,372
it might be responsible for some energy changes that might of the order of 10^-6 of the energy by mass. not only is this the case with a stretched spring but also at atomic levels where some potential energy is associated with every electron.
Atomic energy is not associated with electrons. Potential atomic energy is caused by the mutual repulsion of protons that are held be neutrons. Thus, during fission, the splitting of heavy atom isotopes that are poor on neutrons generate lots of kinetic energy that manifests in the form of heat. Proton repulsion is your "spring" held in place by the neutrons.

#### recca02

Joined Apr 2, 2007
1,214
since the electron is under the influence of attractive forces from protons in nucleus it has a potential energy. this is why a hydrogen electron must be given somewhere around 13.6 eV to come out of the orbit.
that said what is stated in above post is what exactly i wanted to state. At atomic levels there are both kinetic and potential energies so where does that go if the entire mass is converted into energy.
in nuclear reactions momentum and energy are conserved so maybe in this case also something similar might occur maybe a neutrino holds the answer to the momentum conservation part.

about the spring experiment (grinding) i do not think the work required to grind will be same since the material properties change with stretching or compression.
in my opinion it wud be easier to grind a stretched spring (never did something like that before)
i didnt get the second thought experiment it was way over my head.

#### FredM

Joined Dec 27, 2005
124
about the spring experiment (grinding) i do not think the work required to grind will be same since the material properties change with stretching or compression.
in my opinion it wud be easier to grind a stretched spring (never did something like that before)
Ok, I accept the possibility that material properties may change for a stretched spring.. but substitute the spring with 2 hard magnets held apart (potential energy in either repulsive or attractive modes) and there should probably be the same grinding energy requirement, regardless of the potential energy.. But whatever - I would not be satisfied with the result even if I was able to do this experiment.. The E=mc^2 experiment would be far more CONCLUSIVE!

i didnt get the second thought experiment it was way over my head.
I am dissapointed about that.. and so are the Vogons. I understand that a new 'poem' is being penned to comemorate your ignorance.. "Ode to the dematerialised" I believe was the last idea for a title..

#### recca02

Joined Apr 2, 2007
1,214
LOL!
here is something that might confuse u more on that experiment and possibly lead u towards an answer (not sure though),
there seems to be a concept of gravitational (and probably even magnetic) force on photons (which were a result of your mass to energy conversion)

#### FredM

Joined Dec 27, 2005
124
This idea is a bit way out - but it is the only one I can see which could make the 1st law and E=mc^2 both true..
m MUST change as a function of potential energy.
I dont like this idea.. But it may not be as irrational as I first thought. The quantity by which m would need to change would, under normal 'earth' conditions, be extremely small.. I think that potential energy would be transformed into matter at m = E/c^2. I have no idea how this transformation could occur.. But then, I dont really understand how m increases as a function of speed (at c, m becomes infinite ?)

Time to play 'open hand'.. I was hoping that the 1st law was wrong, and that energy could be lost.. I thought that if my spring experiment (particularly the grinding scenario) worked (lost energy) then there was a chance that a simpler, repeatable process could be devised (possibly using nano structures or some clever chemical process).. If this could be done, and energy could be destroyed or lost or made completely unrecoverable, then there was a mechanism to produce cooling.. Imagine, for example, a paint which sucked heat away from the environment and 'destroyed' it.. Science fiction.. But the sort of fiction we badly need right now to have any chance of human survival 50-100 years from now.

Also, if the above was possible, it would make cooling of electronic components a lot simpler.. It could also be used to generate electricity by using it as a thermal sink for a Seebeck device.

Obviously, I am not 100% sure that energy cannot be lost - I understand that there was a lot of 'missing' energy computed for the universe, prior to the discovery of dark matter.. and that Zero-Point energy was devised as a mathematical means of 'balancing the books' .. I do not know what the present state is.. Is there still 'missing' energy and ZPE, o has Dark Matter brought the 'books' back ino balance without requiring ZPE?

#### recca02

Joined Apr 2, 2007
1,214
there is a relation between gravity and density IIRC but i dont think mass changes with gravity.

#### thingmaker3

Joined May 16, 2005
5,084
Have you tried E = Ep + MC^2? MC^2 is only for conversion of mass, after all.

#### FredM

Joined Dec 27, 2005
124
Have you tried E = Ep + MC^2? MC^2 is only for conversion of mass, after all.
Yes.. I thought of this.. BUT, how could Ep be 'contained' in an object?
E = Ep + MC^2 Is what one should get as the result of converting matter with potential energy to energy - It is where I started, and how this question arose.. as I could not see a mechanism to recover Ep. Ep is not 'tangible' E.. So, as I see it, it must either be converted to m, or lost when m is converted to E.

#### thingmaker3

Joined May 16, 2005
5,084
You are assuming instantaneous conversion. If some particles are converted prior to others, then Ep will indeed be released, creating additional heat and some Ek.

#### FredM

Joined Dec 27, 2005
124
You are assuming instantaneous conversion. If some particles are converted prior to others, then Ep will indeed be released, creating additional heat and some Ek.
How? - Let us take an object with gravitational derived Ep, how would converting (say) 50% of its m to E and then a us later converting the remainder to E make any difference to output E?

ok - in practical terms, converting 50% to E would cause an explosive release of energy which would impart kinetic energy into the remaining 50% and, even a us later, the thermal energy released may well recover the total Ep originally in the matter.. But I do not think this is a solution to the question. The question posed assumes instantaneous conversion.. under this condition, E = mc^2, and I cannot see a mechanism for recovery of Ep - unless m has increased proportionaly to its Ep

To re-state the question:
1. Is the 1st law correct?
2. Is E=mc^2 correct?
3. By what mechanism is Ep 'stored' in matter..

Because.. matter m having a potential energy p when instantly converted to energy E by Einstien's equation E=mc^2 does not appear to recover p.

As I see it, for 1+2 to be true, answer (3) can only be that Ep is stored in m as a proportional increase in m.

Alternatively, (1) is not true, and Ep is lost.

Alternatively, (2) is not true, or is incomplete, and there is some other 'factor' held by matter which is proportional to Ep, and some addition required to the formula E=mc^2 (such as E=mc^2 + x where x is the 'other' factor) to make it complete.

At present, I am inclined to believe m is increased proportionaly to its Ep

The problem I have accepting modifications to the original 'experiments' is that I cannot see how potential energy could make any difference to the outcome unless m is changed.. For example, dematerialising matter in 2 steps would produce the same results whether the matter had large Ep or none, as it would for instantaneous dematerialisation, provided m was the same - so to get a different (greater) output for matter with Ep, m must be increased proportionaly to the Ep.

#### thingmaker3

Joined May 16, 2005
5,084
Perhaps the word "recovery" is the problem. How about "lost as waste heat" instead?

#### recca02

Joined Apr 2, 2007
1,214
what are the possible reason for a PE?
gravitational force, magnetic/electric field, nuclear forces and mech configuration (like spring stretching etc).

photons are still not free from gravity.
and since they exhibit a wave like nature i think there is a electrical and mag field accompanying its wave motion. so maybe again a possibility of it having a PE.
the PE due to nuclear forces and mech configuration might manifest itself perhaps in the final energy of the photon as can be deduced from two earlier replies.
in the conversion of mass to energy a lot of possibilities are there like emission of neutrinos which were once supposed to be massless.
i dont claim these answers are exact neither do i have a source to back them but given my knowledge this is the best i can think where the PE goes to.
like MR Sgtwookie wud say they are SWAG .

#### FredM

Joined Dec 27, 2005
124
Thank you all! - I have had all sorts of answers, but no real answers.. Lets face it, its not going to be an easy one to confirm either way! I have posted this question to Scientific American and New Scientist magazines, but had no reply yet.. will let you know if I do get replies.
Perhaps just one other thing to think about .. can anyone think of a way of getting lots of PE into an object easily..?.. I am wondering if it would be possible to do a physical experiment to determine if m increases as a function of PE.. take some matter, weigh it precisely, give it huge Quantity of PE, and weigh it again......

#### recca02

Joined Apr 2, 2007
1,214
might be possible at atomic scale using nuclear forces or keeping a electron at high potential in the order of KV or MV that wud give PE of the order of mC^2. else it wud be hard to get a comparable(to mc^2) amount of PE into a substance.