Despite 180 years of theory on magnetism, it appears that the practice ofcalculating forces on magnetic media is ambiguous, as illustrated by a recentarticle by Casperson. Potentially troubling issues include: Which field B or Hshould be used? Should the total field be used, or only the external field? Andif the latter, what is meant by "external"? Can/should effects of magnetizationcurrents and/or fictitious magnetic poles be included? What is the force ononly a portion of a circuit? We review several well-known approaches tomagnetic force calculations on elements of rigid circuits, and find it veryhelpful to use an explicit example to compare and contrast the various methods.
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