It is hard to observe relativistic effects in everyday life. However, table experiments using a mechanical transmission line for solitons may be an efficient and simple way to show effects such as Lorentz contraction in a classroom. A kink soliton is a deformation of a lattice of several dozen or more pendulums placed on a wire and connected by a spring, or, exactly, a group of pendulums having angles of rotation from 0 to 2 pi. Kink solitons are localized waves that propagate along one space direction with undeformed shape and some particle-like properties. In this paper I will focus on the semirelativistic properties of mechanical kink solitons. The critical velocity of these solitons is not the speed of light, but the speed of linear waves in that certain transmission line. This feature enables everybody to observe phenomena such as length contraction or the relativistic mass-energy relation in a table experiment. Simultaneously, phenomena such as particle-antiparticle interaction can be studied experimentally.