My understanding is that when a charged body receives an
electro-magnetic force the body is accelerated less when it is moving
with respect to the source of the force than when the body is at rest
with respect to the source.
     When V is the velocity of the body in the first case what is the
best evidence that the ratio of the acceleration of the body in that
case to the acceleration in the rest case is (1-V^2/c^2)^.5 rather
than some other factor such as (c-V)/c?  Is the evidence clear that
the direction of the velocity is of no consequence?

---

Request for Question Clarification by hedgie-ga on 11 Jan 2005 13:17 PST

puzzledoldman2-ga

Let's call this factor 1/(1-V^2/c^2)^.5   gamma, as defined here:
http://www2.slac.stanford.edu/vvc/theory/mathfigs/eq-gamma.gif

There are some other definitions on this page 
http://www2.slac.stanford.edu/vvc/theory/relativity.html
which we may find useful.

It seems that your question doubts that force acting on a moving charge
depends on velocity only through this gamma, where only squared magnitude
of velicity vector is present.

That doubt would be well justified, since that force (as noted in the
comment below) does depend on sign of v and not on gamma only.

 That force depends  also on direction of v as illustrated here:

http://www.sr.bham.ac.uk/xmm/fmc1.html

Is this an answer to your question?
If not, then, what is your question? 


Hedgie

---

Clarification of Question by puzzledoldman2-ga on 13 Jan 2005 13:38 PST

I suspect I fouled up in drafting the question by referring to an
electro-magnetic force.  All I was seeking were some references to
empirical data indicating what happens when a Coulomb force passes
between two charged bodies when they are at rest with respect to each
other and when they are moving with respect to each other at a
velocity which is a substantial fraction of c. No magnets were
involved.

     Perhaps it would help to start simply with two positively-charged
bodies one of which is so massive that it's acceleration can be
ignored. Initially there is between the bodies some barrier which
prevents Coulomb force from traveling between the bodies.  The barrier
is then removed.  When the force from the massive body reaches the
smaller body in one case the smaller body is at rest with respect to
the massive body.  In another case when the force reaches the smaller
body at the same distance from the massive body the smaller body is
moving directly away from the massive body at a high velocity.

     Yes, it was my understanding that the now conventional view is
that gamma could be used in expressing the resulting acceleration of
the smaller body in the second case and that the acceleration of the
smaller body would be the same if its velocity had been in any other
direction.

    My question remains "Where can I find references to data
supporting the conventional view?"  Perhaps I should add "Have I
stated correctly the conventional view?"

Your understanding is correct. The factor gamma does enter the
equation of motion for a charged particle
in electromagnetic field and that factor depends only on the magnitude
of the velocity, not on the
direction or sign. That when charged particle is moving in electric
field E or magnetic field B or
when both fields are present. The main point of my previous remark was
that in magnetic fields there
is a factor gamma and also a liner dependence on the velocity vector.
 The factor gamma is relativistic correction - gamma practically when
speed of the particle is small.
 
 In both cases the acceleration depends on mass and mass increases as
velocity starts approaching c.
 Factor gamma describes that relativistic correction. How can this be measured?
 
 Here is a quote:
 
 "Mass Really Does Increase with Speed 


Deciding that masses of objects must depend on speed like this seems a
heavy price to pay to rescue conservation of momentum! However, it is
a prediction that is not difficult to check by experiment. The first
confirmation came in 1908, measuring the mass of fast electrons in a
vacuum tube. In fact, the electrons in a color TV tube are about half
a percent heavier than electrons at rest, and this must be allowed for
in calculating the magnetic fields used to guide them to the screen.
 
Much more dramatically, in modern particle accelerators very powerful
electric fields are used to accelerate electrons, protons and other
particles. It is found in practice that these particles become heavier
and heavier as the speed of light is approached, and hence need
greater and greater forces for further acceleration. Consequently, the
speed of light is a natural absolute speed limit. Particles are
accelerated to speeds where their mass is thousands of times greater
than their mass measured at rest, usually called the "rest mass".
 http://galileo.phys.virginia.edu/classes/252/relativistic_mass.html
 
 While professor Fowler says 'easily' - it has to be taken in context.
Modern particle accelerator
 is a complex machine
 http://www.mindfully.org/Nucs/2002/LBNL-Bevatron-Particle-Accelerator7aug02.htm
 and while the principle is simple (namely charged particle moving in
electro-magnetic field)
 http://science.howstuffworks.com/atom-smasher2.htm
 there is quite a few details. Point is, when the machine is built,
and all calculation done,
 physicist do compare experiment data to the calculation. I will give
you link to some actual data below,
 but first I want to explain why the actual experiment is is more
complex then simple arrangement of the
 thought experiment you described. 
 Large objects, such as tennis balls for example, do not move around
us with relativistic speed.
 May be in space but not here. So, we need to accelerate small things,
like electrons, and to do that,
 we need to place them in vacuum, and perhaps make them go round (like
in a cyclotron) adding some magnets,
 and so on. That's why they end up large an expensive:
 
".. The size of Lawrence's first cyclotron was a mere 4 inches in
diameter. Fermilab has a ring with a beam path of 4 miles. The largest
ever built was the LEP at CERN with a diameter of 8.5 kilometers
(circumference 26.6 km) which was an electron/positron collider. It
has been dismantled and the underground tunnel is being reused for a
proton/proton collider called the LHC due to start operation in 2007"
 http://en.wikipedia.org/wiki/Particle_accelerator
 
 The first one, built in Berkeley was more simple and less expensive
then todays models:
 http://www.aip.org/history/lawrence/epa.htm
 
 
 So, to summaries, please to look at the cartoon on this page
 http://www.aip.org/history/lawrence/cws.htm
 
 Simple, for a particle physicist is - ehmm - involved.
 
 So, if we want the actual data, we will abandon the accelerators and
look at an article
 describing an apparatus which was built so that students can measure
the gamma factor:
 
 http://physics.dickinson.edu/~dept_web/activities/papers/relativity.pdf
 
 Eq (15) contains the gamma   m/m0  and Fig. 10, 11 shows fit to experiments.
 
 
 There are many more cases where the effect was measured.  The problem
with modern physics is that
 it's topic "small particles and very fast particles" are seldom
directly observable. The actual
 cases when we 'see' these effects, such as Alen Belts
 
 http://www-istp.gsfc.nasa.gov/Education/wradbelt.html
 
 GPS satellite signals
 http://www.metaresearch.org/cosmology/gps-relativity.asp
 
  both exhibit relativistic effects, as do  other experiments,on
  6. Tests of Relativistic Kinematics. Some such data are described in
papers referenced here:
  
 http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
 
 
 Hedgie

---

Clarification of Answer by hedgie-ga on 14 Jan 2005 13:06 PST

Correction of a typo:

gamma practically when
speed of the particle is small...


should be

gamma practically equal to 1,  when
speed of the particle is small..

---

Clarification of Answer by hedgie-ga on 14 Jan 2005 13:11 PST

and the 
 
" So, to summaries, please to look .."

should be:

  To summarize, please do look at the cartoon ..."

sory about those typos.

---

Clarification of Answer by hedgie-ga on 15 Jan 2005 06:22 PST

Frankly puzzledoldman2-ga 

    If this is a question (rather then a sigh)

                  " I'm still curious whether .."

 I must say that it is better (next time) to rate the answer only AFTER 
all issues are clarified. (That way a researcher may still hope that
by answering the questions and RFCs well, he may still  achieve the
perfect rating :-)

Anyway.  Physics (same as other sciences) is evolving and curent
theory (SRT) is constantly being challenged and tested by new
applications. Many of the alternative theories, which have been
proposes so far, show lack of understanding and knowledge, but some
are well informed. So far none found a wide following, actually, none
has any serious following at all.

However, it is possible that in the future some corrections will be
needed, as instruments are refined and new areas explored. In the area
and precision currently accessible to us,  SRT formulas work very well
- and have a great advantage of being derived from an elegant and
logical theoretical framework. For this reason Occam razor is likely
to preclude any alternatives.

Changes and  extensions are more likely to be found in GTR - associated with
very strong fields or vast distances which were not mapped as yet, such as,
as an example the (unexplained) Pioneer Anomaly.
 http://www.space.com/scienceastronomy/ mystery_monday_041018.html

Still, just as an example:
If some new theory would PREDICT results of an experiment, and ESA
mission, planned to study the  Pioneer Anomaly would actually confirm
such predicition, which would differ from TR (theory of Relativity) -
then such a new thery would be seriously considered. However, just as
TR is reduced to the Newtonian theory in the limit v/c --> 0, such new
theory would have to reduce to STR in the area, where STR was already
verified.

Hedgie

I'm still curious whether some other factor than gamma would meet the
required criteria.

Guess I?d better not deprive a researcher out of $50. But for a start,
a static electromagnetic (ie magnetic) force doesn?t accelerate
charged particles, it only deflects them. Oscillating electromagnetic
fields (ie radio waves) can and do accelerate charged particles to
good effect. Electrostatic forces accelerate charged particles
directly. You might also check out ?lower and upper hybrid waves?
which are deemed responsible for accelerating charged particles in
Earth?s magnetic field.

But I shall leave it there.

Best

I'm no expert, so I don't know the answer, but I do have a thought on
it (or I guess a "comment").

First, one of the odd things about light is that it is said to always
travel at the same speed in relation to all objects.  So if we are in
an object moving away from a light source, the light would appear
(whatever that means in this case!) to come at us at the same speed as
it would if we were stopped.

Second, light is said to be an electromagnetic wave (search google
for: light electromagnetic wave), and other forms of electromagnetic
waves are said to move at the same speed (just as you have used it in
your formulas).

If the above two items are true, wouldn't other types of
electromagnetic waves share characteristics, such as the part about
them always seeming to move the same speed from all points of view
(like a moving point of view rather than stationary)?  If so, would
your moving, electromagnetically charged vehicle be able to tell the
difference between an electromagnetic field coming from behind while
it is moving vs. when it is stopped (ie, the same net effect on
acceleration)?

This assumes other things too, but I was wondering if that makes you
lean any particular direction or just sounds like a bunch of BS.

I really must not answer this with a comment because researchers need
to eat too. If none pick it up within a few days, suggest you cancel
and re-post including specific researchers in the title. Physics
researchers can be selected by clicking on the blue names and judging
if they are appropriate for your question.

Sorry if this is frustrating.

Best

Hi xcarlx-ga 
        I often wonder about motivation of comments which start with

  IANE =(I'm no expert, and don't know the answer..) but since you say
'I was wondering..' here is a reaction: You are right, in principle: other
emg fields, not just light, behave the same way. Question gets clouded when
one talks about velocity and does not specifies the frame.
 You, it seems, are thinking about velocity of the wave (with respect
to the charge) which is c (in vaccum, and cannot be stopped),
while  v is speed of the charge with respect to some frame of
reference. Usually, frame of reference is chosen so that the SOURCE of
the field
e.g. a permanent magnet is at rest. Then v is a relative velocity (charge
with respect to source) and then there is Lorentz force (a search term) acting
on the charge F~ B x v  - a vector whose magnitude is proportional to velocity. 

The force causes acceleration F/m - and it is a vector again - and
that will bend the path of the charge (same way gravity causes planet
to follow an orbit)
That is used in instruments such as mass spectrograph and cyclotron, so 
it has been amply verified.

And so, guzzi-ga, I think you need not worry about researchers lunches 
(as many of them - sitting at the computer whole day, could benefit
from losing some weight) but should rather pay attention to your
terminology:
You say:
"force doesn?t accelerate charged particles, it only deflects them .." 

Really?

  If there is force, there is acceleration. 
That is the definition of force. 2nd law, remember?
 
 Is it really to necessary to cloud the issue further, by careless comments
(I mean except for benefiting researches  diet)?

Hedgie

Light in a constant velocity does not accelerate or de-celerate. The
energy stream in all spectrums is constant. However, in the
gravitational effect field of super-dense objects, light can "bend" or
be "bent". This can account for the variance of + or - .00010 % in all
energy/mass equation sequence structures. This gives rise to the event
horizon "vortex" and subsequent separation of photo-electron particles
from their "vehicle" in the black-hole phenomena. Because light has
mass, it is 99.9999 % constant.The force causes acceleration F/m - and
that will bend the path of the charge (same way gravity causes planet
to follow an orbit) I STOLE THE LAST LINE OF THIS COMMENT - FROM HEDGIE-GA
VERY WELL STATED !!! $50 TO HEDGIE-GA - HANDS DOWN !!!

Thanks ?hedgie?, but I?m still disinclined to deprive a researcher of
$50, waist-lines notwithstanding (LOL). Magnanimous of you though.

Many a slip twixt cup and lip, ?force? should have been ?field?. Clear
distinction between dyslexia, and carelesness. Not obvious? To impugn
disability is of course admirable :-) :-)

Shall leave it in your capable hands to answer the relativistic
aspects of the question.

Best