*This post was saved to my drafts instead of being posted immediately! Sorry Ken*
As the spring oscillates up and down, the kinetic and potential energy is always exchanging such that the amount of energy in the system remains constant but is split in differing amounts as it moves. When the spring is at the highest and lowest points, the spring has only potential energy (gravitational and elastic respectively). However, as the spring moves between the two points, there is some potential and some kinetic energy. Specifically, as the spring extends from the top to the midpoint, the potential energy decreases as the kinetic energy increases. Then, as the spring uncoils past the midpoint, the kinetic energy decreases as the energy becomes potential again.
