Drag forces in granular materials

Objects moving through granular materials experience a drag force. In the past two decades, many studies have revealed its non-trivial properties, including dependencies on the velocity of the object and the pressure around it. This tutorial review introduces some of these properties and their associated scaling laws. It highlights how they relate to the non-Newtonian behaviour of granular matter, and how they compare to drag forces in Newtonian fluids and other soft materials.