Extra Problem $8.$B The Time$-$Dependent and Time$-$Independent Schr$$dinger Equations Background In classical physics, the motion of a particle can be described for all time once the $$initial conditions$($position$,$ velocity$)$ of the particle$$s motion are known. The so$-$called $$equation of motion$$ in this case is Newton$$s second law. In order to apply Newton$$s second law, one must be able to specify all of the forces acting on the particle in question. In quantum mechanics, the equation of motion is called the