Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnets in an electric field: hidden forces and momentum conservation   In 1967 Shockley and James addressed the situation of a magnet in an electric
field. The magnet is at rest and contains electromagnetic momentum, but there
was no obvious mechanical momentum to balance this for momentum conservation.
They concluded that some sort of mechanical momentum, which they called "hidden
momentum", was contained in the magnet and ascribed this momentum to
relativistic effects, a contention that was apparently confirmed by Coleman and
Van Vleck. Since then, a magnetic dipole in an electric field has been
considered to have this new form of momentum, but this view ignores the
electromagnetic forces that arise when an electric field is applied to a magnet
or a magnet is formed in an electric field. The electromagnetic forces result
in the magnet gaining electromagnetic momentum and an equal and opposite amount
of mechanical momentum so that it is moving in its original rest frame. This
moving reference frame is erroneously taken to be the rest frame in studies
that purport to show hidden momentum. Here I examine the analysis of Shockley
and James and of Coleman and Van Vleck and consider a model of a magnetic
dipole formed in a uniform electric field. These calculations show no hidden
momentum.

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The categories of this paper are: hep-ex
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: math-ph
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The categories of this paper are: solv-int
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ph
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The categories of this paper are: cs