sci.physics.particle

On Feb 18, 9:14=A0am, Zilla wrote:

> But not for you. Modern folks know that mass is energy and
> energy is mass. In earlier days, this is not so intuitive and
> energy needs to be calledrelativistic mass. Now it's called
> total energy which is mass.

I disagree. I believe that this is a common misconception. While they
are proportional for a closed system they aren't always proportional
in the more general case. For instance, place a dielectric in a
uniform electric field. The field will porarize the dielectric and in
so doing induce stress within the dielectric. This stess adds to the
inerial mass (aka "relativistic mass" aka "mass") but the total energy
of the diakectric will not be related to the mass of the dialectric by
E =3D mc^2.

For a solid example please see -- http://www.geocities.com/physics_world/sr/=
inertial_energy_vs_mass.htm

For a textbook explanation of the physics please see "Introduction to
Special Relativity," by Wolfgang Rindler (1982), section 46 which is
entitled "The augmented momentum and mass densities" which starts on
page 149.

This fact seems to have been forgotten by many relativists in the
past. However this fact is becomming more known. A recent text by
Schutz (Gravity from the ground up) explains this as does a recent
article in the American Journal of Physics. The article I speak of is

"The inertia of stress," Rodrigo Medina, Am. J. Phys. 74(11), November
2006

> For example, Kinetic energy and thermal energy is mass.

I disagree. Energy is not mass nor is mass the same as energy. That
which has energy also has mass and that which has mass also has
energy. However they are very different physical quantities
altogether.

>
> > there is jsut one kind of mass!!
>
> In ancient newtonian times, it is.

Actually there were two kinds in Newtonian physics: Inertial mass and
gravitational mass (which is have active and passive types)

Best wishes

Pete

ps - If anyone would like to read the Rindler reference above I'd be
more than happy to send them the relavent pages since I have them
scanned into a file which I have kept.