Re: [Phys-l] Mass and Energy

["Fayngold, Moses" <fayngold@ADM.NJIT.EDU>]

E. Baart has posed 4 points for discussion.                   
  The participants of the Forum have commented on all of them; 
I will only comment on questions 2 and 4.

> 2. Halliday and Resnick state "mass is simply another form of 
energy".

  In my view, this is highly negligent and totally misleading statement.
What will a student learn from it, if understood literally? That, among
varios forms of energy, there is one called mass! Mathematically, this
would mean that, among other things, at least for this form of energy
(let us name it Ef) we would have just Ef = m in ANY system of units.
Which means that this form of energy does not add up to all others, for
which (in conventional system of units) E = mc2, (where m is relativistic
mass). 
  In the wide spectrum of views on the mass-energy relation, the two 
extremes are 
(a) that mass and energy is actually the same thing, and 
(b) that mass and energy represent two different characteristics of
matter - one is the measure of system's inertia, the other is a measure
of system's ability to do work. 
 In case (a) the statement E = mc2 is tautology, in case (b) it is a 
profound insight into the intimate connections between the two different 
characteristics of matter.   
 Regardless of one's position on the spectrum, I do not see a single point
in it that would correspond to the statement >2. Actually, ALL known forms 
of energy are associated with their respective mass with universal scaling 
coefficient c2. A good example, which was already pointed out, is the 
binding energy - it also contributes the corresponding (negative) mass to 
the net mass of a system. 

> 4. One frequently sees statements that matter is converted into 
energy.

  If we define energy as a certain characteristic of matter, the above
statement does not make sense either. An entity is not the same as its 
characteristic or its property. A white chalk cannot convert into whiteness, 
and a dark soot cannot convert into darkness.
  We sometimes do say that in a certain process mass converts into energy
(e.g. "In the process of annihilation mass of a particle and antiparticle is
converted into energy"). 
  It is OK within used professional jargon, but strictly speaking, is a very
poorly worded statement. If mass and energy is the same thing (case (a))
then the statement of one converting into the other is meaningless. If they
are different characteristics (case (b)), then the statement that one converts
into the other is totally wrong (particularly, it contradicts the conservation
of energy). The correct statement would be that the mass of the system
particle + antiparticle becomes the mass of the resulting radiation, and the 
energy of this system converts into the energy of radiation, and the respective 
characteristics are numerically the same before and after the conversion.

Moses Fayngold,
NJIT