For some time I have was having trouble fully understanding what was going on in a journal bearing that is non-lubricated (So that dry friction holds true). Here is what I was having trouble with. Lets say you have something like a spool of heavy cable on a journal bearing, and its being turned at a constant rate with an applied torque. Initially, the spool will rest at the bottom, and the point of contact will be directly in line with the weight vector. But as you increase the moment, the spool will start to 'walk' up the journal thats holding it in place. So its walking up the inside of a circular orifice (to help you visualize it). So as this shaft 'walks' up the journal, the normal force is decreasing. This means the amount of static friction is also decreasing. You will eventually reach a point where it is at maximum static friction. Now you have reached what is known as the 'static friction circle'. But as this moment keeps on steadily increasing to its final value, it will surpass being static friction and start to slip. Now, in the book they say, At first, I thought it would roll up to the limiting case where static friction is maximum, and just start slipping at that same location and stay there; however, after thinking about it for a while, I have come to the conclusion that this is false. I agree fully that it will roll up until some point where it reaches the maximum static friction; however, once it starts slipping, the friction force will drop significantly, but the normal force will stay the same (at that instant). So now you just lost a big component of your force in the tangential direction to sustain equilibrium. So I argue that this thing will start to translate back down the jounral, thus allowing the normal to increase once again. As the normal increases, the kinetic friction force will increase, and it will start to translate back up. And this process should damp out over time until it finally reaches some point A, which is Below where it initially started slipping when static friction gave out. Also, I thought about the possibility of it changing from kinetic back to static friction, and 'walking' back up the jounrnal, but came to the realization that this is impossible. The reason being, in order for it to start rolling without slipping once again, the local velocity has to be zero at the point of contact. But were talking about tolerances here that are a few millimeters at most. So this thing is not going to translate back down at such a speed that it will stop slipping. The final point where it comes to rest can then be considered where the 'kinetic friction circle' occurs, because there is constant relative speed between the jounral and the shaft, and so the angle between the normal and the reaction is [tex] \phi_k [/tex]. Am I wrong, or does this sound like reasonable logic to anyone? Somehow, I'm very temped to say im right, because I thought long and hard about this. http://sns.chonbuk.ac.kr/manufacturing/bearing-9.jpg The picture sucks, but its the best I can find online. Appologies.