Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electromagnetic Force and the Maxwell Stress Tensor in Condensed Systems   While the electromagnetic force is microscopically simply the Lorentz force,
its macroscopic form is more complicated, and given by expressions such as the
Maxwell stress tensor and the Kelvin force. Their derivation is fairly opaque,
at times even confusing, and their range of validity all but a well kept
secret. These circumstances unnecessarily reduce the usefulness and
trustworthiness of some key quantities in macroscopic electrodynamics.
  This article presents a thorough yet pedagogical derivation of the Maxwell
stress tensor and electromagnetic force in condensed media. It starts from
universally accepted inputs: conservation laws, thermodynamics and the Maxwell
equations. Simplifications are considered for various limits, especially the
equilibrium, with a range of validity assigned to each expression. Some
widespread misconceptions are scrutinized, and hidden ambiguities in popular
notations revealed.
  A number of phenomena typical of strongly polarizable systems, especially
ferrofluid, are then considered. In addition to enhancing the appreciation of
these systems, it helps to solidify the grasp of the introduced concepts and
derived formulas, and it demonstrates the ease with which the Maxwell stress
tensor can be handled, inviting theorists and experimentalists alike to embrace
this useful quantity.

37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
2
The categories of this paper are: math