Experiments were conducted to determine the effect of vibration on friction. A rider, consisting of three fixed 1/3-inch diameter balls, slid along a flat steel plate under a dead weight load of 1 kg and a speed of 0.02 cm/second. The plate was vibrated by a speaker at frequencies of 20, 100, 500, and 1000 cycles per second. Acceleration, coefficient of friction, and electrical resistance of a contact were measured. For both lubricated (white oil plus oleic acid) and unlubricated conditions, apparent kinetic friction decreased rapidly after the acceleration of vibration approached and exceeded the acceleration due to gravity. Electrical resistance increased periodically with vibration. The data indicated that the vibration periodically reduced metal-to-metal contact due to reduced load. Thus, an apparent reduction of the coefficient of friction was observed. Microscopic observation of the unlubricated wear tracks on the plate showed absence of galling, brown film formation, and marked plastic deformation during sliding with vibration. The possibility of fretting-type oxide film was considered.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis. Minnesota, October 18–20, 1966.