angle of friction: meaning, definition, pronunciation and examples

For dry, cohesionless granular materials, they are often numerically identical and the terms are used interchangeably. However, in precise geotechnical engineering, the 'angle of internal friction' is a shear strength parameter determined from tests, while the 'angle of repose' is a physical observation of a poured pile. For cohesive materials, they differ.

It varies widely: smooth metal on metal might be less than 10°, sand can range from 30° to 45°, angular crushed rock can be over 40°, and for rough concrete on soil, it can approach 25°-35°.

Common laboratory methods include the Direct Shear Test (DST) or the Triaxial Shear Test for soils and granular materials. For solid interfaces, an inclined plane test can be used, tilting the plane until sliding initiates.

It is fundamental for calculating earth pressures on retaining walls, the stability of natural and engineered slopes (like dams or excavations), the design of foundations, and the analysis of fault mechanics in geology.

The angle between the resultant force and the normal force when an object is on the verge of sliding on a surface, equal to the arctangent of the coefficient of friction.

Angle of friction is usually formal, scientific, engineering in register.

Angle of friction: in British English it is pronounced /ˈæŋɡl̩ əv ˈfrɪkʃn̩/, and in American English it is pronounced /ˈæŋɡl̩ əv ˈfrɪkʃn̩/. Tap the audio buttons above to hear it.