Two disks are mounted on low-friction bearings on a common shaft. The first disc has rotational inertia I and is spinning with angular velocity w .

Two disks are mounted on low-friction bearings on a common shaft. The first disc has rotational inertia I and is spinning with angular velocity w . The second disc has rotational inertia 2I and is spinning in the same direction as the first disc with angular velocity 2w as shown. The two disks are slowly forced toward each other along the shaft until they couple and have a final common angular velocity of: