Our experiment shows that the electrons at fixed place can exert both repulsion and attraction to the negative charges in the same time but at two sides of a boundary called critical radius, where the linear velocity of the electrons’ precession is equal to light speed. This is an uncovered natural law called Critical Cylindrical Effect (CCE) deduced from rotational relativity and proved by the experiments made in our lab. Ten screenshots of the experimental video are given in this paper. This experimental result denotes that both Coulomb’s law and the spin theory of quantum mechanics are incomplete. As an application of CCE, the strong interaction between two protons in nucleus is introduced. It just is the electromagnetic interaction suffered from CCEs of spin and precession.