y charge moving in magnetic field exp force???

When a charged particle is not moving the electric field lines emanate from the charge outward in all directions and until we move the charge we might think this is the only kind of field that the charge can create. When the charge moves, we find that there is the possibility for a new kind of field that can have lines which do not start or end on charges, but which can form closed loops. These are the magnetic field lines. As soon as there is movement of the charges, there is time changes of the electric fields, and that can produce magnetic fields.

There is really no profound answer other than the fact that the electromagnetic field has 6 different degrees of freedom and that it requires the electric and magnetic field to represent these. Also when objects are moving relative to each other, the two fields can mix together.The force is due to the interaction.