Linear ball-bearing motor

The acceleration of a steel ball running on parallel steel rails has been measured. When the rails are connected, respectively, to the positive and negative terminals of a DC supply, the ball completing and electrical circuit, the acceleration increases as the current is raised. Three components of acceleration have been recognised: a frictional retardation; an electromagnetic acceleration which increases with current but is independent of speed; and an electromagnetic retardation which increases with both current and speed. The characteristics of this linear ball-bearing motor are compared with those of the cylindrical ball-bearing motor, and with the predictions of electromagnetic theories