  We experimentally and theoretically study impacts into dense cornstarch and
water suspensions. We vary impact speed as well as intruder size, shape, and
mass, and we characterize the resulting dynamics using high-speed video and an
onboard accelerometer. We numerically solve previously proposed models, most
notably the added-mass model as well as a class of {viscous-like} models. In
the {viscous-like models}, the intruder dynamics are dominated by {large,
viscous-like forces} at the boundary of the jammed front {where large shear
rates and accompanying large viscosities are present.} We find that our
experimental data are consistent with this class of models and inconsistent
with the added mass model. Our results strongly suggest that the added-mass
model, which is the dominant model for understanding the dynamics of impact
into shear-thickening dense suspensions, should be updated to include these
viscous-like forces.
