Re: Opposites.

[Leigh Palmer <palmer@sfu.ca>]

> > > Two oppositely charged particles traveling in opposite directions
> > > along parallel paths? Whoops, which kind of "oppositeness" rules?
> > [Don Simanek]
>
> > Hah! got tangled in your rules, eh? They attract, of course
> >
> > Your point is correct; your example is, unfortunately, ill-chosen.
> > The reason, of course, is that currents going in the *same*
> > direction attract, what is known as the "pinch effect". The pinch
> > effect is itself a fine Gegenbeispiel. In that case "Likes attract."
> >
> > Leigh

To which Brian Whatcott replies:

> I suspect it is Leigh who has been caught. One may accept the pinch
> effect, but then argue like this:
> a moving particle does not have to represent a current.

It certainly informs my concept of current! What do you use
instead?

> If oppositely charged particles travelling in opposition attract,
> then one could assume that similarly charged particles travelling
> in convoy would also attract ( via the double negative ).

Agreed; and they do. They also repel one another by electrostatic
force, and the net force is repulsive. It is, of course, smaller
than the repulsive force between two static charges - even though
the electric field at each charge is stronger when the charges are
moving.

This effect is the standard demonstration of the connection between
electric and magnetic fields in relativity. The reduced mutual
repulsion of like charges moving along parallel paths can be
attributed to the magnetic attraction between them. One can also
note that they accelerate away from each other less rapidly because
of relativistic mass increase. When considered from the comoving
frame they appear to diverge faster "because" the comoving clock is
running slow! The comoving observer is deceived!

I think Brian is incorrect here, but I'm open to other arguments.

Leigh