The angle of repose is an engineering property of granular materials. The angle of repose is the maximum angle of a stable slope determined by friction, cohesion and the shapes of the particles. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area, and coefficient of friction of the material. Material with a low angle of repose forms flatter piles than material with a high angle of repose. In other words, the angle of repose is the angle a pile forms with the ground.
An alternative measurement, useful for many of the same purposes, is testing with a specialized instrument called a shear cell
The larva of the antlion traps small insects such as ants by digging a conical pit in loose sand, such that the slope of the walls is very close to the angle of repose for the sand. Thus when a small insect blunders into the pit, its weight causes the sand to collapse below it, drawing the ant toward the center where the antlion larva lies in wait. The antlion larva assists this process by vigorously flicking sand out from the center of the pit, when it detects a disturbance, undermining the pit walls and causing them to collapse toward the center, bringing the prey with them.
The angle of repose plays a part in several topics of technology and science, including: