Wheels, Shafts and Axles Rotate in Bearings. The roller became a wheel only when it could be safely positioned by a bearing assembled to the vehicle frame. The history of the wheel is thus inseparably linked with the history of the bearing.
Since there is no model in nature for guiding wheel on axles or axle journals, man faced a great technical task in designing bearings – a task which has not lost its importance and attraction to this day. As it seems to us today, everything started quite simple.
In the center of the wheel there is a circular bore. Into this bore the axle, axle journal or bearing journal are inserted. As with all motion , a moving part slides on a stationary part. The relative motion between the two surfaces in sliding contact is measured as the sliding friction , this friction must be overcome