sorry, this is is a general question about a conceptual definition I read in my textbook, i hope that's ok. "an object that rolls without slipping at a constant velocity over a surface with friction experiences no frictional force" is this true? i understand that on a frictionless surface, the object wouldn't need any external force or torque to keep it rolling, but on a surface with friction, why would the same situation apply? and, in addition, how does an object slip while it has angular velocity? does that mean that for every instant that a particle is in contact with the ground, it slides for an infinitesmall distance? I don't get how that could happen from a macroscopic view.