  We discuss the form of the wave-function of a state subjected to a scalar
linear potential, paying special attention to quantum tunneling. We analyze the
phases acquired by the evolved state and show that some of them have a pure
quantum mechanical origin. In order to measure one of these phases, we propose
a simple experimental scenario. We finally apply the evolution equations to
re-analyze the Stern\&Gerlach experiment and to show how to manipulate spin by
employing constant electric fields.
