Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The falling pencil: a "Divertimento" in four movements   The dynamics of a simple pencil with a tip laid on a rough table and set free
to fall under the action of gravity is scrutinized as a pedagogic case study.
The full inquiry is anticipated by a review of three other simplified movements
foreshadowing its main features. A few exact and general results about the
sliding angles and the critical static coefficient of friction are established.

4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
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The categories of this paper are: math
22
The categories of this paper are: chao-dyn
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas