Ok, so I got a spring attached to a weight and positioned on the eqm point. So I displace it a little and it undergoes oscillation. At the lowest point, everything is Elastic Potential Energy since extension is maximum. At the eqm point, extension=0 so it is just a mixture of KE and GPE. At the top, there is 0 KE, maximum GPE. But what about the Elastic Potential energy? Does the hooke's law extension formula includes 'compression'? Is there 'compression energy'? Thanks.