Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Angular Momentum of Rockets, Balloons, and Other Variable Mass
  Systems   Variable mass systems are a classic example of open systems in classical
mechanics. The reaction forces due to mass variation propel ships, balloons,
and rockets. Unlike free constant mass systems, the angular momentum of these
systems is not of constant magnitude due to the change in mass. In this paper,
we show that the angular momentum vector for such a system has a fixed
direction in space and, thus, is partially conserved for both rigid and
flexible, torque-free, variable mass systems. A potential use of this result is
that it provides a suitable stationary reference frame against which the
orientation of variable mass system could be measured.

14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
0
The categories of this paper are: hep-ph
11
The categories of this paper are: hep-lat
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph