I personally have never gotten the hang of yo-yos. However, I can still appreciate all of the physics behind them. For instance, yo-yos have two forms of potential energy. The first is that by holding it up in the air, it is given the potential to fall to the ground. The second is that the it has string wound around it, which gives it the potential to spin as it unwinds. When the yo-yo is released, these two forms of potential energy are both changed to kinetic energy. Also, the spinning of the yo-yo is an example of centripetal force.