Abstract
A steel ball dropped on loose, very fine sand creates a jet
which can exceed the release height of the ball.
Our experiments show that the series of events
is as follows:
On impact of the ball, sand is blown away in all directions
(``splash'') and an impact
crater forms. When this cavity is collapsing, a jet emerges
and is driven straight into the air. In the sand, an air bubble has formed
which rises slowly towards the top, causing a granular eruption.
We address the problem and the phenomenon by first comparing
it
with similar effects in liquid.
We then show the results of molecular dynamics simulations and
construct a simple continuum model for this system which shows the
same features as seen in experiment.
Finally,
we examine
the role of the air for the phenomenon and
present results on impact events on the same sand in vaccuum.
Surprisingly, the jet is getting much weaker.
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