Angle of Repose | Angle Repose

The angle of repose or the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.

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 shapes of the particles, and the coefficient of friction of the material. However, a 2011 study shows that the angle of repose is also gravity-dependent. Material with a low angle of repose forms flatter piles than material with a high angle of repose.

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 μ_s between the surfaces.

Famous quotes containing the words angle of, angle and/or repose:

“So much symmetry!
Like the pale angle of time
And eternity.
The great shape labored and fell.”
—N. Scott Momaday (b. 1934)

“The inhabitants of earth behold commonly but the dark and shadowy under side of heaven’s pavement; it is only when seen at a favorable angle in the horizon, morning or evening, that some faint streaks of the rich lining of the clouds are revealed.”
—Henry David Thoreau (1817–1862)

“I grow savager and savager every day, as if fed on raw meat, and my tameness is only the repose of untamableness. I dream of looking abroad summer and winter, with free gaze, from some mountain-side,... to be nature looking into nature with such easy sympathy as the blue-eyed grass in the meadow looks in the face of the sky. From some such recess I would put forth sublime thoughts daily, as the plant puts forth leaves.”
—Henry David Thoreau (1817–1862)