The relativistic length contraction effect and changing distance effect produce 2 different magnetic forces. Together they form complete magnetic force.

I have derived 2 magnetic forces with Coulomb’s law and charges’ velocity. The first force dFlc is derived in «Length-contraction magnetic-force between arbitrary currents». The second force dFcd is derived in «Changing distance effect». dFlc and dFcd are added together to give the expression for complete magnetic force dFcm.

Please read the article at

Coulomb magnetic force

PDF http://pengkuanem.blogspot.com/2018/03/coulomb-magnetic-force.html

or

Word https://www.academia.edu/36278169/Coulomb_magnetic_force

PDF Changing distance effect http://pengkuanem.blogspot.com/2018/03/changing-distance-effect.html or

Word https://www.academia.edu/36272940/Changing_distance_effect