The objective of this simulation is to help understanding of conception ?Potential Barrier?. The forces of two types appear at interaction of particles ? the long-range repulsive forces and short-range attractive forces. As a result the potential of interaction represents not monotonic function of distance between particles. The region under graphics of this function is called the potential barrier. Its characteristics (a height and a width) depend on energy of particles, which are in potential wells (see the ?Potential wells? simulation also). In this activity studding conception is demonstrated as interaction of a matter wave with a potential barrier. It is possible in quantum mechanics, where the particle may be considered as the wave and there wave function ψ(x) makes sense of particle possibility to be in given point of space at defined time. A particle (matter wave) with energy E travels from left to right in a region with potential barrier. Use floating band controls to very the value of particle energy, the height U0 and width L of the barrier and calculate the probability of the particle being transmitted past the barrier T. You can note, that although the transmission probability is low it is possible for the particle to tunnel through the large potential barrier and reappear on the opposite side. This phenomenon is a hallmark of quantum mechanics; it is called a tunnel effect and forms the basis for numerous technological devices.