The direction of Coulomb's force and the direction of gravitational force in the 4-dimensional space-time

In this paper, we point out that the 4-vector force acting on a particle is always in the direction orthogonal to the 4-vector velocity of the particle in the 4-dimensional space-time, rather than along the line joining the particle and the action source. This inference is obviously supported from the fact that the magnitude of the 4-vector velocity is a constant. This orthogonality brings out many new aspects for force concept. In this paper it is found that the Maxwell's equations can be derived from classical Coulomb's force and the orthogonality, some gravitational effects such as the perihelion advance of planet can also be explained in terms of the orthogonality.