Abstract
An important case is the scratching on the car body caused by a passing truck with one of the nuts (or bolts) sticking out of the wheel rim. In such a case the scratch marks have special shapes. When the rim and the tyre diameter of the scratching vehicle is known, the dimensions of the scratch shape are sufficient to determine the relative velocity of the two vehicles. If the velocity of one of the vehicles is known, one can also determine the duration of the contact and the velocity of the other vehicle, information which could be interesting in police or insurance investigations.