A current carrying wire in a constant magnetic field.
We show here a moving wire which is coming out of the
screen, and carries current out of the screen, as it
moves into a constant vertical magnetic field. The wire
feels a force to the left, which is a combination of
a magnetic pressure to the right in front of the wire
which pushes it back to the left, and a magnetic tension
to the left behind the wire, which pulls it back to
the left. Because of the stresses associated with the
magnetic field (both its own field and the constant
field), the wire slows down and comes to rest, and then
accelerates back in the direction from whence it came.
The currents which produce the constant field (not shown)
absorb the momentum of the wire as it reverses, and
this produces a force on those sources which is to the