  Although the gravity dependence of granular friction is crucial to understand
various natural phenomena, its precise characterization is difficult. We
propose a method to characterize granular friction under various gravity (body
force) conditions controlled by centrifugal force; specifically, the
deformation of a rotated granular pile was measured. To understand the
mechanics governing the observed nontrivial deformation of this pile, we
introduced an analytic model considering local force balance. The excellent
agreement between the experimental data and theoretical model suggests that the
deformation is simply governed by the net body force (sum of gravity and
centrifugal force) and friction angle. The body-force dependence of granular
friction was precisely measured from the experimental results. The results
reveal that the grain shape affects the degree of body-force dependence of the
granular friction.
