When materials do not stick together well under pressure, such as sand, they are described as being what?

When materials do not adhere well to each other under pressure, they are described as cohesionless. This term specifically refers to materials, like sand, that lack internal forces of attraction, which are necessary for particles to bond tightly together. Because these materials do not stick well, they can easily shift and flow, leading to less stability when compressed.

Cohesive materials, on the other hand, possess attraction between their particles, allowing them to hold together more firmly under pressure. Elastic and ductile refer to the ability of materials to deform under stress and then return to their original shape or to stretch without breaking, respectively, and are not applicable to the bonding characteristics of grains in cohesionless materials. Thus, “cohesionless” accurately describes the behavior of materials like sand when subjected to pressure.