  Laboratory experiments and numerical simulation reveal that a submerged
intruder dragged horizontally at constant velocity within a granular medium
experiences a lift force whose sign and magnitude depend on the intruder shape.
Comparing the stress on a flat plate at varied inclination angle with the local
surface stress on the intruders at regions with the same orientation
demonstrates that intruder lift forces are well approximated as the sum of
contributions from flat-plate elements. The plate stress is deduced from the
force balance on the flowing media near the plate.
