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BEGIN:VEVENT
DTSTAMP:20261018T010034Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20070320T191500Z
DTEND:20070320T210000Z
UID:event67@bu.edu
URL:http://physics.bu.edu/internal/events/show/67
SUMMARY:Unified force law for impact cratering in loose granular media
DESCRIPTION:Featuring Doug Durian\, U. Penn\nHosted by: Sidney Redner\n\nPa
	rt of the Physics Department Colloquia Series.\n\nExperiments on the low-sp
	eed impact of solid objects into granular media have been used both to mimi
	c geophysical events and to probe the unusual nature of the granular state 
	of matter.  Observations have been interpreted in terms of conflicting stop
	ping forces: product of powers of projectile depth and speed; linear in spe
	ed; constant\, proportional to the initial impact speed; and proportional t
	o depth.  This is reminiscent of high-speed ballistics impact in the 19th a
	nd 20th centuries\, when a plethora of empirical rules were proposed.  To m
	ake progress\, we developed a means to measure projectile dynamics with 100
	 nm and 20 us precision.  For a 1-inch diameter steel sphere dropped from a
	 wide range of heights into non-cohesive glass beads\, we reproduce prior o
	bservations either as reasonable approximations or as limiting behaviors.  
	Furthermore\, we demonstrate that the interaction between projectile and me
	dium can be decomposed into the sum of velocity-dependent inertial drag plu
	s depth-dependent friction.  Thus we achieve a unified description of low-s
	peed impact phenomena and show that the complex response of granular materi
	als to impact\, while fundamentally different from that of liquids and soli
	ds\, can be simply understood.  This work was done in collaboration with Dr
	. Hiroaki Katsuragi.
LOCATION: \, \, 
STATUS:CONFIRMED
CLASS:PUBLIC
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