One of the most popular models for describing friction is the Coulomb friction model. This model defines coefficients of static friction μ μ s ∈ ∈ R and dynamic friction μ μ d ∈ ∈ R such that μ μ s > μ μ d . These coefficients describe the two types of friction forces in terms of the reaction forces acting on the bodies. More specifically, the static and dynamic friction force magnitudes f s , f d ∈ ∈ R are computed in terms of the reaction force magnitude f r = | f r | as follows