Abstract In general a single “coefficient of friction” is inadequate to define the fractional resistance between contacting bodies. It is necessary to know both the inclination of the resultant force line and the offset of this line from the theoretical point of contact. This paper presents results of experiments, which were made to determine the effects of velocity on the inclination, and the offset of the line of action of the resultant force between two disks in peripheral contact. The results indicate that the sliding velocity is of primary importance in determining the inclination of the line of action of the resultant force. It is the sum of the sweep velocities that is of primary importance in determining the offset of the resultant force line. The nature of the relationship between the angle of inclination and the offset of the line of action of the resultant force, and the proximity of the contact conditions to those existing for pure rolling, was investigated but no conclusive results were obtained.