The friction angle is a measure of the resistance to sliding between two surfaces in contact. It is commonly used in fields like civil engineering and geology to describe how materials, such as soil or rock, behave under stress. The angle is typically expressed in degrees and is derived from the ratio of the shear stress to the normal stress acting on the surfaces. In practical applications, the friction angle helps engineers design stable structures, such as retaining walls and foundations. A higher friction angle indicates greater resistance to sliding, which is crucial for ensuring safety and stability in construction projects. Understanding this concept is essential for predicting how materials will interact under various loads.