Angle of repose
When bulk granular materials are poured onto a horizontal surface, a conical pile forms.
The term has a related usage in mechanics, where it refers to the maximum angle at which an object can rest on an inclined plane without sliding down.
This angle is equal to the arctangent of the coefficient of static friction μs between the surfaces.
[citation needed] If the coefficient of static friction μs is known of a material, then a good approximation of the angle of repose can be made with the following function.
A simple free body diagram can be used to understand the relationship between the angle of repose and the stability of the material on the slope.
There are numerous methods for measuring angle of repose and each produces slightly different results.
This method is appropriate for fine-grained, non-cohesive materials with individual particle size less than 10 mm.
The cylinder is rotated at a fixed speed, and the observer watches the material move within it.
[6][7] The larvae of the antlions and the unrelated wormlions Vermileonidae trap small insects such as ants by digging conical pits in loose sand, such that the slope of the walls is effectively at the critical angle of repose for the sand.
Thus, when a small insect, commonly an ant, blunders into the pit, its weight causes the sand to collapse below it, drawing the victim toward the center where the predator that dug the pit lies in wait under a thin layer of loose sand.
The larva assists this process by vigorously flicking sand out from the center of the pit when it detects a disturbance.
The combined effect is to bring the prey down to within grasp of the larva, which then can inject venom and digestive fluids.
The angle of repose is related to the shear strength of geologic materials, which is relevant in construction and engineering contexts.
[9] For granular materials, the size and shape of grains can impact angle of repose significantly.
As the roundness of materials increases, the angle of repose decreases since there is less friction between the soil grains.
It is important for many civil and geotechnical engineers to know the angle of repose to avoid structural and natural disasters.
[11] The angle of repose plays a part in several topics of technology and science, including:
