Re: What kind of energy denotes E in Einstein's 1905 Sep 27paper?
- From: valls@xxxxxxxxxxx
- Date: Fri, 28 Sep 2007 19:44:56 -0700
On 28 sep, 20:40, "Pmb" <some...@xxxxxxxxxxxxx> wrote:
<va...@xxxxxxxxxxx> wrote in messageWhy you refer to the internal structure of the body? See what Einstein
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On 28 sep, 19:59, "Pmb" <some...@xxxxxxxxxxxxx> wrote:
<va...@xxxxxxxxxxx> wrote in message
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Exactly 102 years ago (1905 September 27) Einstein wrote a very short
paper. Einstein starts referring to a body at rest with energy E. I
want to know what kind of energy is that E. Being the body at rest,
the kinetic energy is excluded. Then, what other kind of energy a body
at rest can have in 1905?
RVHG (Rafael Valls Hidalgo-Gato)
The energy that left the body was in the form of radiation. I.e. the
radiation carried away the mass.
Pete
Hello Peter. You are right, a little ahead Einstein writes about some
quantity L of light emitted from the body. But I am referring to the
energy E_0 of the body at rest before that.
The energy of a body may have different forms. E.g. it might consist a box
with three compartments in it. One of the compartments, the middle one,
consists of two charged particles being held together by a spring which is
latched in the closed position. In the body the other two compartments there
are ideal gases which have only kinetic energy. The container and partitions
are made up of atoms which have rest mass and are held together by bonds
whose associated energy also has mass. So for this body there are several
kinds of energies: Potential, EM, Kinetic, Atomic bonds, rest mass of atoms.
Suppose the latch broke. The charges would accelerate apart and would create
EM raddiation by the accelerating charges. Due to a loss of EM energy out of
the box(which is a closed system) there will be a total decrease in the mass
of the box.
writes
{The kinetic energy of the body with respect to S' diminishes as a
result of the emission of light, and the amount of diminution is
independent of the properties of the body}
Einstein is referring here to the inertial frame S' where the body is
seen moving with v velocity. The kinetic energy here only depends on
v, being totally independent of the internal properties of the body.
Besides, see what Einstein writes when he arrives to his general
conclusion:
{If a body gives off the energy L in the form of radiation, its mass
diminishes by L/c^2. The fact that the energy withdrawn from the body
becomes energy of radiation evidently makes no difference, so that we
are led to the more general conclusion that
The mass of a body is a measure of its energy content}
The general conclusion is totally independent of the withdrawn energy
form. The possible internal structure of the body is totally
irrelevant here. See how the energy withdrawn from the body is seen in
system S' as a diminution in its kinetic energy, only dependent on the
velocity v the body has as a whole entity and totally independent of
any internal structure. See also how the energy E of the body (that is
total energy in system S) is present also without changing its value
in system S (E is a relativistic invariant). What kind of energy is
then this E that when added to the kinetic energy K is equal to the
total energy H the body has in system S'?
Why you need to refer to specific energy forms? Einstein result isOr you thing that when a
body emits light the energy must be necessary also in light form
before the emission?
No. A body could do work on its environment. I could transfere thermal
energy through heat conduction to another body and thus the mass associated
with the heat energy (i.e. the kinetic energy of the particles which are in
the box and which make up the box) leaves the box.
totally general, not depending on energy forms, but including all
kinds of them (including the unknown ones in 1905). And the energy E
that a body as a whole entity at rest have in 1905 has a very specific
denotation: potential energy.
RVHG (Rafael Valls Hidalgo-Gato)
Pete- Ocultar texto de la cita -
- Mostrar texto de la cita -
.
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