Hi,I'm in the Second Semester of my undergraduate course of Mechanical Engineering....at present,we have the analysis of certain simple mechanical devices,which work based on friction. Please help me in the following concepts..... 1.In a journal bearing (practically seen in the rail road tyres),the axle's two ends are placed in the tyres of the train.....does the axle really move up the hub of the wheel, or is it just a mathematical consideration ? Also,according to the aricle http://www.manchesteruniversitypress.co.uk/uploads/docs/310101.pdf [Broken], 4th page,3rd paragraph,it says "The reaction force, reac, which is applied by the wheel, has its point of application to the left of the line of action of axle relative to an observer looking in the directionof that line ( since the axle climbs in the hub of the wheel due to the effect of axle friction as the rotation of the wheel is impending). At that state, the equilibrium equation Summation of F =0 is still applicable and it results in Faxle = Freac.".......I din't understand why reaction force, which is applied by the wheel, has its point of application to the left of the line of action of axle ." Also,what is the circle of friction of the axle? Thanks in advance for any help!