work can be done by magnetic forces?Or can it not?

Well, can magnetic forces do work or not?The discussions on this topic seem to go on ad nauseum, but one thing that a majority seem to agree upon is that the magnetic (Bqv) part of the Lorentz force cannot do work on an unconstrained(or even constrained,depending on your point of view) moving charged particle.To be more precise there is no movement of the charged particle in the direction of the force.Looking at it another way ,the application of the magnetic force alone does not result in any energy changes.

Assuming that the magnetic field (Bqv) cannot do work on the particle does it mean that it cannot do work on anything?There seem to be many people who answer this question in the affirmative.Despite this it is easy to imagine events where work is done.Consider the following:

An observer is in a frame of reference such that there is a system setting up a B field which is observed to be stationary.A particle of charge q and velocity v then enters the field such that  it experiences the Bqv force. As a result the particle moves in its curved path.
All the time there is the force on the particle there is an equal and opposite force on that part of the system that sets up the B field (Newton's third law).The result is that this system moves from its initially observed state of rest.Due to momentum considerations this movement may be considered to be negligible but nevertheless there is movement and a transfer of energy.
If you are one of those who believe that the magnetic can not do work then here is just one of the questions that arises.What is the force/mechanism that is instrumental in the magnetic system picking up kinetic energy?

(Of course the whole event is much more involved than merely that which has been described above but I couldn't be bothered to write any more about it at the moment)

rest mass variability

Try googling the title above or variations  of  it and you will come up with hits.The possibility that rest mass of particles can vary has been given some consideration ,particularly it seems in relation to gravitational theory.

Something that seems to have both been recognised yet strangely overlooked(or given scant consideration) is the strong possibility,based on well established experimental evidence that rest masses of particles in electrical fields,depends on the structure of the field in terms of the locations of the interacting particles.In short,particles such as electrons and protons have rest masses which are frame dependant.The rest mass of a particle depends on the structure of the rest frame and the location of the particles within it.

At this point a lot of physicists might dismiss the idea claiming that it is at odds with special relativity.Such dismissive claims are easily rejected.It is easy to show that the concept of a frame dependant rest mass is not at odds with relativity at all.In fact it is special relativity that provides the strongest evidence that rest mass is variable.The variability referred to here is incredibly small and in general hardly makes any difference to those problems solved by using relativity.Small though the variability is(perhaps better described as negligible in most applications)the variability can be measured and has been measured.

Does variability disprove special relativity?In short the answer is no.

More to come tomorrow