Theoretical question with practical implications (trying to model yarn as mass points connected with spring systems and need to get collision response with objects right): A mass point approaches a plate under an angle. You have the coefficient of restitution β and the friction coefficient μ. You know the initial speed v of the point and can decompose it in normal component vN and tangential component vT to the surface. What is the collision response of the mass point? Just inverting the sign of vN and multiplying with β? Or is there also a friction response since technically the surface and mass point exert forces on each other in an infinitely small amount of time, so an impulse reaction, and I also need to add -μ*vN to the tangential component or something?