In a previous work, we studied the flow of rice grains out of a cylindrical silo with a vertical barrier that divided the grains in equal compartments. We now revisit similar experiments, but using spherical or conical "obstructions". In most of the tested configurations, spheres and cones do not really mean an obstruction. On the contrary, they become facilitators of the flow of the grains. The maximum value of the velocity of flow of the grains does not depend so heavily on the kind of "obstruction". A more important contribution comes from the initial heights of the "obstruction". All these results can be easily replicated in the classroom.
granular materials; dynamic properties
