🚀 go-pugleaf

 Harry: 

 >>
 >>   Newton's third law fails only when an object is moving at a velocity
 >> which is much larger than the propagation of a signal through the object
 >> and large enough for the simultaneity of different points on the object to
 >> matter. Then, newton's third law doesn't really fail so much as it needs
 >> to be analyzed more carefully to account for the difference in
 >> simultaneity.
 >
 >I must read the allegations again! It is not just about high velocity, but
 >force balance with the Lorentz force, for example when a charged object
 >moves slowly perpendicular to a wire with a DC current. Perhaps I missed out
 >on a textbook that carefully analyses this simple looking case.
 
  The motion of a charge next to a wire can be found in a fairly
straight-forward way just by finding the B-field from the wire and
and using the lorentz force law. (Working in the frame in which the
field from the wire is purely magnetic). 


 >
 >>   I'm not really sure what you mean by ampere's law needing newton's third
 >> law. Anpere's law doesn't contain any forces. You need the lorentz force
 >> law for that. Neither ampere's law nor any of the other maxwell equations
 >> even describe charges, moving or stationary.
 >
 >Sorry, perhaps Ampere had several laws?!
 >I meant the Ampere force law, which is very roughly:
 >
 >F = -i_m * i_n *(dm . dn / r^2) * (2 cos phi - 3 cos a cos b)
 
  I didn't realize ampere had a "force law" other than what could
be derived from the usual equations. In any case, that expression
is written in a particular frame (which is okay). But, notice that
because it's derived under the assumption of infinitely long wires,
it's rather unphysical (at least from a relativistic standpoint),
since the current can't ever begin flowing or stop flowing, but
had to have existed and continue to exist for all time.


 >See for example
 >http://ieeexplore.ieee.org/iel1/27/6502/00256790.pdf?isNumber=6502&arnumber=
 >256790&prod=JNL&arSt=701&ared=713&arAuthor=Graneau%2C+N.
 
 That doesn't work for me. I get a login page which tells me I have to
register for a web account. As matter of general principle, I do not
access web sites that require providing personal information of any
kind.