Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Normal Force and Static Friction Acting on a Rolling Ball
  Actuated by Internal Point Masses   The goal of this paper is to investigate the normal and tangential forces
acting at the point of contact between a horizontal surface and a rolling ball
actuated by internal point masses moving in the ball's frame of reference. The
normal force and static friction are derived from the equations of motion for a
rolling ball actuated by internal point masses that move inside the ball's
frame of reference, and, as a special case, a rolling disk actuated by internal
point masses. The masses may move along one-dimensional trajectories fixed in
the ball's and disk's frame. The dynamics of a ball and disk actuated by masses
moving along one-dimensional trajectories are simulated numerically and the
minimum coefficients of static friction required to prevent slippage are
computed.

16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci