Turn of the One-Dimensional Direction in the Physical Space for a Periodic Particle

An invariant definition of the world line (of a particle) in the Minkowski 4-space corresponding to a periodic motion of a particle in the physical 3-space is given. A sharp lower estimate for the turn of the one-dimensional direction of the particle in the physical space as for a function of the velocity of the particle is obtained. Bibliography: 6 titles.