Question: why are the coefficients of static and kinetic friction different

title: Friction
text: Static friction is friction between two or more solid objects that are not moving relative to each other . For example , static friction can prevent an object from sliding down a sloped surface . The coefficient of static friction , typically denoted as μ , is usually higher than the coefficient of kinetic friction . Static friction is considered to arise as the result of surface roughness features across multiple length - scales at solid surfaces . These features , known as asperities are present down to nano - scale dimensions and result in true solid to solid contact existing only at a limited number of points accounting for only a fraction of the apparent or nominal contact area . The linearity between applied load and true contact area , arising from asperity deformation , gives rise to the linearity between static frictional force and normal force , found for typical Amonton - Coulomb type friction .