Hi guys.
From a person by the posting name of Bilge, I copied this part of the
conversation: "photon has relativistic mass m =hf/c^2."
My apologies for the ignorance, what exactly does relativistic mass mean?
Does this mean that if photon was not traveling, it would no have mass, or
does this mean that regardless of whether or not it's moving, it has as you
guys call it relativistic mass? Sorry again, but for years I could never get
why a wave/particle such as those of the EMR do not have mass, how could
they than have energy and so on. Now I kind of got used to the fact that
this is true, yet could someone please explain the concept to me of
relativistic mass of the EMR particles/waves and so on, and do particles
alone have relativistic mass, and what about the waves alone as well.

"Zarkovic" wrote in message
news:QFGsb.382116$9l5.123709@pd7tw2no...
Hi guys.
From a person by the posting name of Bilge, I copied this part of the
conversation: "photon has relativistic mass m =hf/c^2."
My apologies for the ignorance, what exactly does relativistic mass mean?

That is the term that some people use when they refer to inertial mass in
relativity. Relativistic mass is defined as the ratio of momentum to
velocity. I.e. relativistic mass is the "m" in p = mv. Actually mass is
defined such that mv is conserved. Then the quantiy p = mv is defined as
'momentum'

In order to energy to be conserved in electrodynamics an electromagnetic
field must have an energy density to it. That is Poynting's theorem -- For
derivation see
http://www.geocities.com/physics_wor...ng_theorem.htm

In order for momentum to be conserved in electrodynamics the EM field must
have momentum. For derivation see -
http://www.geocities.com/physics_wor...n_momentum.htm

The momentum density, g, is related to the energy density, u, as g = u/c.
Therefore for a finite amout of radiation E = pc. According to the above
definition of mass, anything with a non-zero momentum density must have a
non-zero mass density rho. Therefore

g = rho*v

For light v = c. Therefore g = rho*c. Substiture in g = u/c to get u/c =
rho*c --- rho = u/c^2. For a finite about of radiation m = E/c^2. This
relation was first derived by Poisson in 1900 (for what he called a
'fictitious fluid') and a few years later derived again by Einstein in 1906
in the second part of a paper called "The Principle of Conservation of
Motion of the Center of Gravity and the Inertia of Energy," Albert Einstein,
Annalen der Physik 20 (1906)

For a definition and derivation of "relativistic mass" aka "inertial mass"
see
http://www.geocities.com/physics_wor...rtial_mass.htm.

Does this mean that if photon was not traveling, it would no have mass, ..

A photon can never be at rest so the question can't be answered. However
since all the energy of a photon is kinetic energy so if somethign which is
all kinetic energy has no kinetic energy and since a particle at rest has no
momentum then the mass of that thing would be zero. Such a particle does not
exist which satisfies this property of zero-energy though.

does this mean that regardless of whether or not it's moving, it has as
you
guys call it relativistic mass? Sorry again, but for years I could never
get
why a wave/particle such as those of the EMR ...

What is "EMR"?

An electromagnetic wave also has "relatvistic mass."

"Zarkovic" wrote in message news:QFGsb.382116$9l5.123709@pd7tw2no...
Hi guys.
From a person by the posting name of Bilge, I copied this part of the
conversation: "photon has relativistic mass m =hf/c^2."
My apologies for the ignorance, what exactly does relativistic mass mean?

The term "relativistic mass" is not commonly used, nor is it's the
value.
It is the value you get when you set E = total energy, and solve E = m
* c^2 for m. Some people find the quantity appealling because it
allows you to retain the Newtonian formula for momentum.

Does this mean that if photon was not traveling, it would no have mass,

Photons always travel. They cannot exist except travelling at c.
Note also, that the word 'mass' when used without a qualifier
generally refers to 'invariant mass' (previously called 'rest mass'),
not 'relativistic mass'.

or
does this mean that regardless of whether or not it's moving, it has as you
guys call it relativistic mass?

See above.

Sorry again, but for years I could never get
why a wave/particle such as those of the EMR do not have mass, how could
they than have energy and so on.

There is no answer to that. It's simply what is observed.

Now I kind of got used to the fact that
this is true, yet could someone please explain the concept to me of
relativistic mass of the EMR particles/waves and so on,

See above.

and do particles alone have relativistic mass,

Sure.

and what about the waves alone as well.

I don't know what "waves alone" means.

Paul Cardinale

P.S. Watch out for PMB, he uses non-standard terminology and insists
that it is correct.

Zarkovic:
Hi guys.
From a person by the posting name of Bilge, I copied this part of the
conversation: "photon has relativistic mass m =hf/c^2."

You didn't get that from my part of the conversation, unless I
qualified with some caveats. That sort of idea leads to all sorts
of misconceptions.

My apologies for the ignorance, what exactly does relativistic mass mean?

It means that someone is doing newtonian physics that has been
patched up to account for the finite speed of light.

Does this mean that if photon was not traveling, it would no have mass, or
does this mean that regardless of whether or not it's moving, it has as you
guys call it relativistic mass?

If by "you guys", you mean those of us that are physicists, "us guys"
don't use "relativistic mass" in general and the term finds only limited
applications in casual conversations, none of which involve photons. It's
best to just forget about it when trying to understand relativity.
Relativity is a theory about invariance and the quantities which are
part of the theory proper are invariant quantities. The mass of an
object is defined to be its "rest mass", because the properties of
an object in its rest frame are the properties of an object which
are invariant. The photon has no rest frame because it has no mass.

We already have a quantity that means the same thing as "relativistic
mass". It's the energy. The energy is a frame dependent quantity and
isn't very useful unless you also know the invariant properties of
your particles. etc.

Sorry again, but for years I could never get
why a wave/particle such as those of the EMR do not have mass, how could
they than have energy and so on. Now I kind of got used to the fact that
this is true, yet could someone please explain the concept to me of
relativistic mass of the EMR particles/waves and so on, and do particles
alone have relativistic mass, and what about the waves alone as well.

Best to forget about "relativistic mass". It leads to precisely the
kind of confusion. Any time you see "relativistic mass", read it as
"energy" and then remember that "energy" consiststs of kinetic energy
and "rest mass energy", i.e., E^2 = (pc)^2 + (mc^2)^2. The quantity
E here is what might occasionally be called "relativistic mass" if it
happens to be expedient in some particular circumstance. If you find
posts on the newsgroups in which "relativistic mass" is used and if you
are confused by it, just ignore the post as it either addresses some
specific question in which its use is expedient and presumably those
discussing it realize it's only an expedient, or else its use is due
to a misunderstanding of relativity.

Thanks guys, by the way, EMR=electro-magnetic radiation.

(Paul Cardinale) wrote

Watch out for PMB, he uses non-standard terminology and insists
that it is correct.

Nonsense. That's simply a bald faced lie posted by an ignorant person

(Paul Cardinale) wrote

The term "relativistic mass" is not commonly used, nor is it's the value.

That is incorrect. You've been listening to bilge and waite for
waaaaay too long. Proof to the contrary is readily found in

American Journal of Physics --
"Apparatus to measure relativistic mass increase," John W.
Luetzelschwab, Am. J. Phys. 71, 878 (2003)
"Relativistic mass increase at slow speeds," Gerald Gabrielse, Am. J.
Phys. 63, 568 (1995)
[Online at - http://hussle.harvard.edu/~gabrielse...icMassAJP.pdf]
"In defense of relativistic mass," T. R. Sandin, Am. J. Phys. 59, 1032
(1991)

Other journal -
"Observed Relativistic Mass Increase for 0.3 eV Electron", G.
Gabrielse and H. Dehmelt, Bull. Am. Phys. Soc. 25, 1149 (1980).

Modern SR/GR/Cosmology texts -

"Cosmological Principles," John A. Peacock, Cambridge University
Press, (1999)
"Relativity: Special, General and Cosmological," Rindler, Oxford
Univ., Press, (2001)
"Basic Relativity," Richard A. Mould, Springer Verlag, (1994)
"Introducing Einstein's Relativity," Ray D'Inverno, Oxford Univ.
Press, (1992)

It is the value you get when you set E = total energy, and solve E = m
* c^2 for m.

Wrong. A particle be moving in an EM field such that the total energy
is constant and yet the relativistic mass-energy is not. "total
energy" and mc^2 are not the same thing.

Some people find the quantity appealling because it
allows you to retain the Newtonian formula for momentum.

That's not why its used.

Note also, that the word 'mass' when used without a qualifier
generally refers to 'invariant mass' (previously called 'rest mass'),
not 'relativistic mass'.

Wrong. Examples to the contrary are found throughout recent relativity
literature.

Several examples contrary to cardinale's claims can be found listed at
http://www.geocities.com/physics_wor...istic_mass.htm

Please don't make comments like this - they are obviously wrong.

(Bilge) wrote

If by "you guys", you mean those of us that are physicists, "us guys"
don't use "relativistic mass" in general ..

This is a lie. Pay no attention to him. Check out the counter examples
I've listed to bilge's claims.

"Zarkovic" wrote in message news:QFGsb.382116$9l5.123709@pd7tw2no...
Hi guys.
From a person by the posting name of Bilge, I copied this part of the
conversation: "photon has relativistic mass m =hf/c^2."
My apologies for the ignorance, what exactly does relativistic mass mean?
Does this mean that if photon was not traveling, it would no have mass, or
does this mean that regardless of whether or not it's moving, it has as you
guys call it relativistic mass? Sorry again, but for years I could never get
why a wave/particle such as those of the EMR do not have mass, how could
they than have energy and so on. Now I kind of got used to the fact that
this is true, yet could someone please explain the concept to me of
relativistic mass of the EMR particles/waves and so on, and do particles
alone have relativistic mass, and what about the waves alone as well.

There are also numerous examples of usage in the relativity
literature. E.g. one application pertains to the center of mass of
radiation. This is actually a homework problem in "Classical
Electrodynamics - 2nd Ed.," J.D. Jackson. If you have this text then
the problem is on page 617. It's problem 12.16(b). It pertains to
conservation. I've done this out and placed the solution on the web at

http://www.geocities.com/physics_wor...nservation.htm

bilge doesn't know what "center of mass" means as it pertains to
electromagnetic energy so he was unable to understand the question. He
was therefore both unable to solve it and unable to understand the
solution when it was shown to him

See also
http://www.geocities.com/physics_wor...er_of_mass.htm

Pmb

Subject: Relativistic mass of EMR particles/waves
From: (Gauge)
Date: 11/13/03 2:55 PM US Mountain Standard Time
Message-id:

(Paul Cardinale) wrote

Watch out for PMB, he uses non-standard terminology and insists
that it is correct.

Nonsense. That's simply a bald faced lie posted by an ignorant person



And that is pmb's responce to everyone when everyone keeps telling him that he
is wrong.