Answer: When the yo-yo is in your hand, its kinetic energy is equal to zero, and its gravitational potential energy is the largest. Throw the yo-yo out of your hand and start to move down while spinning, faster and faster, and the kinetic energy is getting bigger and bigger. At the same time, the yo-yo keeps falling with its position, and its gravitational potential energy is decreasing. In this process, its gravitational potential energy is continuously converted into kinetic energy. When the yo-yo turns to the lowest point, its kinetic energy is the largest. At this time, the yo-yo rotates fastest and rises along the rope. As the yo-yo rises, its rotation speed becomes slower and slower. At this time, the kinetic energy of the yo-yo is continuously converted into potential energy, so the yo-yo can be thrown back into its hands again.