  This paper presents an intuitive, geometrical derivation of the relativistic
addition of velocities, and of the electromagnetic interaction between two
uniformly moving charged particles, based on 2 spatial + 1 temporal dimensional
Minkowski diagrams. We calculate the relativistic addition of velocities by
projecting the world-line of the particle on the spatio-temporal planes of the
reference frames considered. We calculate the real component of the electro-
magnetic 4-force, in the proper reference frame of the source particle,
starting from the Coulomb force generated by a charged particle at rest. We
then obtain the imaginary component of the 4-force, in the same reference
frame, from the requirement that the 4-force be orthogonal to the 4-velocity.
The 4-force is then projected on a real 3 dimensional space to get the Lorentz
force.
