How do you calcuate angle of friction given cohesion value?

The angle of friction (φ) can be calculated using the cohesion value (c) and the internal friction angle (ϕ) of the material. The relationship is described by the Mohr-Coulomb failure criterion, which states that the shear strength (τ) can be expressed as τ = c + σ * tan(ϕ), where σ is the normal stress. To find the angle of friction, you can rearrange this equation or use trigonometric relationships based on the given cohesion and stress values, typically requiring additional information about the normal stress acting on the material.