The idea is that transfer of momentum between atoms is a good approximation of current. In that sense, the difference in shell momentum, on average, can be th

The idea is that transfer of momentum between atoms is a good approximation of current. In that sense, the difference in shell momentum, on average, can be thought of as potential or voltage. Like the hydraulic analogy, this visualization is to help us understand not an exact movie of what's happening. Math may be better for that level of detail, for now. This visualization uses atoms, which is the main advantage over the hydraulic.