Physics Colloquium
Friday, January 30th, 2004 4 P.M.
E300 Math/Science Center
Peter Schiffer
Pushing through the sand: Penetration and drag in a granular
medium.
The motion of a solid object being pulled slowly through a granular
medium
is resisted by jamming of the grains, resulting in a drag force
which
differs dramatically from viscous drag in a fluid both in its average
properties and in having large fluctuations. We have studied the
drag
force and its fluctuations as a function of the velocity, the depth
in the
medium, the geometry of the dragged object, and the grain size
and
morphology. The drag process provides an excellent test-bed for
the
strength of locally jammed states among the grains and the effects
of
confinement on the jamming. Recent work has focused on the effects
of
solid barriers within the grains on penetration of a granular medium.
We
find that the surface texture of the solid barrier impacts the
depth
dependence of the resistance as the barrier is approached. Furthermore,
there is a clear length scale to the effect of a solid barrier
which has
an unusual characteristic dependence on system parameters.
Physical Review Letters 82, 205 (1999); Physical Review Letters
84 5122
(2000); Physical Review E 64, 031307 and 64, 061303 and 64, 061303
(2001); Nature (in press, 2004)
Refreshments 3:30 P.M. Room E200 Math/Science Center
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