This is possible because they are given potential energy by the electric field.
You have put potential energy into the wall just by leaning on it.
The strong force has potential energy, just as gravity and spring forces do.
The third term is the potential energy when the field has any given magnitude.
In this case, U is the potential energy of q+.
This means that the effect of the circulation is to increase the potential energy.
Potential energy seems to be stored in the force between objects.
The amount of potential energy in water is proportional to the head.
The potential energies for all sources can simply be added.
Also the work done by a conservative force is equal to the negative of change in potential energy during that process.