Why the yoyo can automatically return to the palm of the hand?
Yoyo is a very interesting exercise toy. When playing yoyo, hold the end of the string with its hand on its short shaft, then throw it downwards. The yoyo will follow the momentum of each round of the coil around it, loosen, and spin. When the entire string has been pulled straight, the yo-y will turn upwards again and cause the coil to wrap around the short shaft in the opposite direction until it returns to the palm. Drop the yoyo down again; it will return, so on, repetitive, how interesting.
Why can the yoyo automatically return to the palm of your hand?
There is an important knowledge of physics here; that is, kinetic energy and potential are interchangeable. When the yoyo is in the palm of its hand, its kinetic energy is zero, the greatest potential. When it was thrown from its hand, the yoyo started to spin and move downwards, and under the influence of gravity, the faster it turned. The kinetic energy is constantly growing, and at the same time, with the relentlessly low momentum of the yoyo, the potential energy is constantly decreasing. Then the potential of the yoyo changes into kinetic energy. By the time the yoyo turns to the lowest point, its kinetic energy is greatest, the smallest potential. At that time, the yô yô turned fastest. After reaching the lowest point, the yo will turn upwards along with the coil, winding the short shaft in the opposite direction. Following the upward momentum of the yoyo, its rotation speed is getting slower and slower. The yo’s kinetic energy of the yoyo is constantly transformed into potential energy until it reaches the highest point. The spinning motion stops, its kinetic energy is zero, and the potential energy is greatest.
Based on the law of conservation of mechanical energy, when there is no external force or the external force’s workforce produces zero, the object’s total mechanical energy does not change. Thus, the yoyo must return to the original position. But, in the upward and downward motion, the yoyo will lose part of its energy due to air resistance and friction between the rope and the short shaft. Without additional energy, the yoyo will not reach its original height. So, when playing the yo y must have certain tricks, constantly adding a little energy. How to replenish energy? When the yoyo spins to the lowest point, the string is about to begin winding upwards, at that moment pulling the string upwards with one hand, making the yoyo spin speed a bit faster, increasing some energy. Thus, the yoyo can up, down, down forever.