4
$\begingroup$

How does a (static) magnetic field accelerate objects (like an iron nail) if we are taught that the magnetic force does always zero work?

$\endgroup$

marked as duplicate by Emilio Pisanty, Chris, Kyle Kanos, stafusa, Pieter Feb 16 '18 at 18:50

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ Who taught you that?? Electrical motors run on magnetic forces. $\endgroup$ – Pieter Feb 15 '18 at 18:02
  • 4
    $\begingroup$ There's a good discussion of this in Chapter 8 of the most recent edition of Griffiths's Introduction to Electrodynamics; but unfortunately I don't have it in front of me to summarize. I'll try to remember to do so next time I have the book in front of me and some free time. $\endgroup$ – Michael Seifert Feb 15 '18 at 19:17
  • $\begingroup$ @MichaelSeifert The discussion in Griffiths is very good, and it's not wrong; however, it's one of several instances where Griffiths avoids mentioning some additional subtleties. Magnetic fields acting on current do no work, but magnetic fields also interact with intrinsic spins; it then becomes a matter of precisely how you define "work" when such spins are involved whether the magnetic forces are doing work or not. -Brett $\endgroup$ – Buzz Feb 15 '18 at 20:27