* Magnetic fields exert forces on moving charges: The fundamental principle is that magnetic fields interact with moving charges. A stationary charge doesn't experience a magnetic force.
* Direction matters: The direction of the magnetic force is determined by the direction of the charge's motion, the direction of the magnetic field, and the sign of the charge.
* Right-hand rule: A common way to visualize this is with the right-hand rule. Point your thumb in the direction of the charge's velocity, your fingers in the direction of the magnetic field, and the palm of your hand will point in the direction of the magnetic force.
In summary, a charged particle must have a non-zero velocity to experience a magnetic force.
