Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A vehicle with a two-wheel steering system mobile in shallow dense
  granular media   We design a vehicle with a steering system made of two independently
rotatable wheels on the front. We quantify the effectiveness of the steering
system in the mobility and maneuverability of the vehicle running in a box
containing a layer ping-pong balls with a packing density 0.8, below the random
close packing value 0.84 in 2D. The steering system can reduce the resistance
exerted by the jammed balls formed ahead of the fast-moving vehicle. Moreover,
if only one of the two steering wheels rotates, the vehicle can turn into the
direction opposite to the rotating wheel. The steering system performs more
efficiently if the wheels engage the ping-pong balls better by increasing the
contact area between the wheels and the balls. We advocate applying our design
to machines moving in granular materials with a moderate packing density.

18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex