Abstract: For a microscopic particle in a centrally symmetric potential and in its stationary bound state, there is a relationship about the expectation value of the force to the particle. In this paper, several different proofs to this relationship are presented with a discussion to its physics connotation. In addition, the conditions necessary for the relationship to hold is discussed, hence the related misunderstanding or inaccuracy currently in literature is clarified.

Key words: centrally symmetric potential, stationary bound state, relationship