Summary
A new method for measuring normal forces under a granular packing
is introduced. A high precision
electronic balance is used to measure normal forces on individual
beads at the bottom of a granular material. Due to the high sensitivity
of this setup the normal forces on individual beads
without applying any external load on the system were measured.
From these measurements the distribution of forces, the response to small
perturbations at grain level and the spatial
correlation between normal forces were investigated at the bottom of
the packing.
The distribution function is consistent with a power-law with
an exponent a=0.3 for small forces. At large forces
a cross over to an exponential decay is observed with
a decay constant b=1.8.
Small amplitude spatial correlations were observed
in the normal forces at the bottom of the pile, and
the radial pressure distribution was dependent
of the different filling procedures.
Finally we report on systematic relaxations in the
measured weight as function of time on single grains
at the bottom of the packing after perturbing the system.
Show full description
