A disk defamation horizontally on a frictionless, mass less, rotational motion support such that the disk is spinning freely about a vertical axis through the centre of the disk and perpendicular to the face of the disk. A second disk the same to the first disk is held in place a negligible height immeasurably close however not touching above the first disk. The second disk is aligned therefore perfectly with the first disk that the axis of rotation of the first disk also passes through the centre of the second disk. The person embracing the second disk drops it onto the first disk and the two disks spin as one. Is mechanical energy preserved in this process?