  The ability of a person to run on the surface of a suspension of cornstarch
and water has fascinated scientists and the public alike. However, the
constitutive relation obtained from traditional steady-state rheology of
cornstarch and water suspensions has failed to explain this behavior. In a
previous paper, we presented an averaged constitutive relation for impact
rheology consisting of an effective compressive modulus of a system-spanning
dynamically jammed structure (arXiv:1407:0719). Here, we show that this
constitutive model can be used to quantitatively predict, for example, the
trajectory and penetration depth of the foot of a person walking or running on
cornstarch and water. The ability of the constitutive relation to predict the
material behavior in a case with different forcing conditions and flow geometry
than it was obtained from suggests that the constitutive relation could be
applied more generally. We also present a detailed calculation of the added
mass effect to show that while it may be able to explain some cases of people
running or walking on the surface of cornstarch and water for pool depths $H
>1.2$ m and foot impact velocities $V_I> 1.7$ m/s, it cannot explain
observations of people walking or running on the surface of cornstarch and
water for smaller $H$ or $V_I$.
