A student attaches a block of mass M to a vertical spring so that the block-spring system will oscillate if the block-spring system is released from rest at a vertical position that is not the system’s equilibrium position. The figure shows three positions of the spring as it travels from point X to point Y and then from point Y to point Z. Point X is the lowest point of the center of mass of the block as it oscillates. Point Y is the equilibrium position of the block-spring system. Point Z is the highest point of the center of mass of the block as it oscillates. The gravitational potential energy of the block-spring-Earth system is considered to be zero at point X.