# Magnetic force on charges moving parallel with equal velocity

As we know when charges moving in an magnetic field experiences a force but what if both the body causing the field the charge under consideration moves with same velocity?....Correct me if I am wrong if we consider any external frame than it is justifiable that force acts on charges body but what if we take the charge as frame of refernce

If you have an electric charge $Q$ moving with velocity ${\bf v}$ with respect to some inertial frame through a magnetic field ${\bf B}$ created by, say, a bar magnet stationary in that frame, then the force acting on the charge is ${\bf F} = Q {\bf v} \times {\bf B}$. You appear to be asking about what happens in the rest frame of the charge? Here the charge is at rest so you might be tempted to argue "shouldn't the force be zero"? It appears that in one frame there is a force and in another there is no force.