About: Phil Metzger (former co-founder NASA KSC Swamp Works) spent 25 years deriving that gas-flow sand entrainment flux is the ratio of two — the aerodynamic lift force over the submerged grain weight. This lab makes that ratio literal: drag-coupled grains physically hop when τ* crosses the Bagnold critical curve, and the live Shields θ, Bagnold τ*, and particle Reynolds Re* update continuously.