In this video I will give an overview of the barrier and compare how a particle reacts in a quantum mechanical world to the classical mechanical world. In classical mechanics when a particle comes upon a barrier where the potential of the barrier is greater than the energy of the particle, then 100% of the particle will reflect off the barrier. In quantum mechanics that is not the case. Depending on the energy of the particle and the potential of the barrier, a certain percentage of the particle will make it through or reflected off the barrier.