  Shear induced alignment of elongated particles is studied experimentally and
numerically. We show that shear alignment of ensembles of macroscopic particles
is comparable even on a quantitative level to simple molecular systems, despite
the completely different types of particle interactions. We demonstrate that
for dry elongated grains the preferred orientation forms a small angle with the
streamlines, independent of shear rate across three decades. For a given
particle shape, this angle decreases with increasing aspect ratio of the
particles. The shear-induced alignment results in a considerable reduction of
the effective friction of the granular material.
