In general, the electric and magnetic fields are functions of the position and time. Therefore, explicitly, the Lorentz force can be written as: F ( r ( t ) , r ˙ ˙ ( t ) , t , q ) = q [ E ( r , t ) + r ˙ ˙ ( t ) × × B ( r , t ) ] in which r is the position vector of the charged particle, t is time, and the overdot is a time derivative.