Energy in mass spring system.
As the mass oscillate there is exchange of three types of energy GPE, EPE and KE. At the lowest point where the spring is fully extended the EPE is at its max. and GPE is at it's minimum and KE is zero as the mass has zero velocity. As the mass moves up, there is a increase in KE and GPE but a decrease in EPE. At its equilibrium point, the KE is a max. As it continues above the equi. pt the KE and EPE decrease leading to an increase in GPE. As its highest point the mass has no KE but the GPE is a max and EPE is a minimum. The exchange of energy is ongoing but the total energy remain the same throughout the oscillation.