On top of the hill, the red object has a positive potential energy and it can move down the potential gradient at increasing speed. On the flat surface the object has zero potential energy, but can move freely if it has some kinetic energy. In the well, the object is confined by its negative potential energy. It can vibrate backwards and forwards with kinetic energy, but can't get out of the well until it is given enough potential energy or it vibrates enough to jump out. Potential Energy and Force Work done by a force produces an increase in kinetic energy .
Work done against a force produces an increase in potential energy .
In solids, there are attractive forces pulling the atoms together and also repulsive forces that prevent the atoms from getting too close. If the repulsive force were not present then solids would collapse in on themselves. To describe the forces between atoms, we need an electric potential energy function that gives a potential well with both attractive and repulsive terms. These were drawn using the data. J N Notice that the two graphs have the same general shape.