at the beggining of basic mechanics, we learned about friction, moreover we distinguish between static and dynamic friction. there is something quite disturbing: when an object on an inclined rod is static we can say that the static friction is holding it in place. now, whe we push the object up the rod, somtimes instead of stoping in place, the object slips down the rod, in the same incline that it was static without the movement up. if we assume that we live in sequential world, then in some point the object was static again. so how can we explain the difference between the two? sorry for my bad grammer..