Intrusion into Granular Media Beyond the Quasistatic Regime

The drag force exerted on an object intruding into granular media can depend the object's velocity as well depth penetrated. We report intrusion experiments at constant speed over four orders in magnitude together with systematic molecular dynamics simulations beyond quasi-static regime. find that dependence crosses to a characteristic time after initial impact. This crossover scale, which depends penetration speed, depth, gravity and intruder geometry, challenges current models assume additive contributions drag.