There is a rotating shaft which is in contact with a spherical ball. The ball is in contact with an outer casing.The casing is fixed to the ground. I want to estimate the life of the surface which is in contact. There are two surfaces i want to estimate the life for. 1)surface of the rotor which is in contact with the ball 2)surface of the casing which is in contact with the ball. Which surface will wear faster? Any proof of this. Which subject i should concentrate on ( i think mechanics or rotational mechanics-any web site for this) to understand this process.