Euler's disk. This apparatus illustrates the dynamic system of a spinning disk on a flat surface (such as a spinning coin). It consists of a steel disk and a rigid mirrored base which provides a low-friction surface. The disk, when spun, exhibits a spinning rolling motion, slowly progressing through different rates and types of motion before coming to rest. The change in orientation of the disk's axis of symmetry accelerates as the disk spins down. The energy of the system dissipates mainly as a result of rolling friction when the coin slips along the surface. This phenomenon was studied by Leonhard Euler in the 18th century.