When two consistent, unlubricated surfaces slide against each other, there is a specific, predictable amount of friction that occurs. This amount increases as velocity does, but only up to a certain point. That increase generally follows what is known as a Stribeck curve, after Richard Stribeck. On the other hand, if the two surfaces are completely lubricated, there is no direct friction or rubbing at all. In real life, though, there is often a situation where the surfaces are not completely dry, but also not so lubricated that they do not touch.