From: raicu@netcom.com (Eugen Raicu)
Subject: Re: E=mc2?
Date: Thu, 03 Sep 92 05:47:22 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
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jac@ds8.scri.fsu.edu (Jim Carr) writes:
: In article <1992Sep1.041046.7302@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
: >dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
: >: gross@maxwell.ucsc.edu (Mike Gross) writes...
: >: >But nuclear weapons _do_ turn matter into energy.   ....
: >: 
: >: Springs do the same thing. A compressed spring has kx^2/2c^2 more mass than
: >: a relaxed one. So releasing a spring turns mass into energy.
: >: 
: >That's right. So to say that nuclear weapons are connected with E=mc^2
: >makes about as much sense as saying that your bedsprings are nuclear
: >powered. 
: 
: No.  Bedsprings are atomic powered.  ;-) 
: 
: The real point, if my memory is correct, is that the connection between 
: nuclear weapons and E=mc^2 arose because of the role of Einstein's letter 
: (composed by Szilard) to Roosevelt on the need for a nuclear weapons 
: program.  What I do not recall, and keep forgetting to check at home 
: where one of my books contains a copy of said letter, is whether the 
: formula appears in it.  In any case, the reporting after the first 

I would be a little disappointed with Einstein if the formula appears in it.

: explosion was made public made much of the conversion of mass to energy 
: according to the new (still very new at that time) formula and it is 
: this news coverage that makes the association so strong. 
: 
: >         In all these instances, all we have is energy  being converted
: >to other forms of energy. Of course I am neglecting
: >particle-antiparticle things, but I am told that in fission bombs most
: >of the energy comes from releasing nuclear binding ENERGY. Correct me if
: >I am wrong about this.
: 
: Yes and no.  It is the change in binding energy, not the actual disappearance 
: of particles as would be the case in a matter-antimatter explosion, that 
: is the source of the energy released.  However, the change in binding 
: energy is measureable as an actual change in total mass of the stuff you 
: had before and have after the reaction.  I think total fission of 1 kg 
: of U-235 gives a reduction in mass by about 1 gram, if memory is accurate. 
: (200 MeV is about 1/4 of an amu, so about 1/1000 of total mass)
: 
: Binding energy is deduced from the mass differences; it is not 
: something you can see directly any more than one can see the actual 
: kinetic and potential energies of the various constituent particles 
: at any given instant.  After all, the nucleus is a complicated many-body 
: system that does not have a fixed number of particles: it can contain 
: Deltas or nucleon-antinucleon pairs as part of its wavefunction, as 
: well as the neutrons and protons one finds when one takes it apart. 

In the case of nuclear reactions, it is convenient to deduce the binding
energy from differences in rest masses. In the case of bed springs,
it is convenient to measure it mechanically. In both cases the total
mass of the system is conserved, as is the total energy. In both
cases the higher potential energy configuration has a correspondingly
higher rest mass than the lower potential energy configuration. The
kinetic and electromagnetic energies and the relativistic masses of
the lower potential energy configurations make up for the lower
potential energies and the lower rest masses.

I don't see any fundamental differences between nuclei and bed springs.
Correct me if I am wrong about this.

: 
: --
: J. A. Carr                                    |  "The New Frontier of which I  
: jac@gw.scri.fsu.edu                           |  speak is not a set of promises
: Florida State University  B-186               |  -- it is a set of challenges."
: Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)
-- 
Eugen Raicu
raicu@netcom.com
Xref: sparky sci.physics:13718 sci.math:10654