This Demonstration shows the time-evolution of the wavefunction for a particle in a linear potential field (in units with ℏ=1), representing a constant external force. The initial state is a Gaussian wave packet. Only the real part of the complex wavefunction is plotted. In agreement with its classical behavior, the particle is accelerated to the left. You can also see the probability density function; quantum mechanically, the probability density function is the absolute square of the wavefunction.