fig excitation force that causes resonance spring-mass system with sliding friction body with mass is attached to spring with stiffness while sliding on plane surface the body is also subject to friction force due to the contact between the body and the plane figure depicts the situation the friction force can be modeled by coulomb friction mgu mgu where is the friction coefficientand mg is the normal force on the surface where the body slides this formula can also be written as mg sign /profig sketch of one-dimensionaloscillating dynamic system subject to sliding friction and spring force