Who will lift himself up?

Legend has it that one day, in order to show his bravery and strength, Xiang Yu, the overlord of Western Chu, selected some strong men in the army to compete with him. Compared to what? It's very interesting. Everyone sits on a chair and sees who can grab the chair with both hands and lift himself up. As a result, everyone else failed, and only Xiang Shuyu won. So, Xiang Yu really lifted himself? No, according to Newton's third law, when two objects interact with each other, the action and reaction forces between the objects are always equal in magnitude and opposite in direction, acting on the two objects respectively. If you directly lift yourself with your hands, your hands will act on you and it will be an object that belongs to you and you will not be able to lift it without external force.

What about sitting in a chair? Sitting on a chair, Xiang Yu's body is subject to two forces: the attraction of the earth and the supporting force of the chair. These two forces are equal in magnitude and opposite in direction, and act in a straight line. Therefore, the two forces are balanced, and Xiang Yu can sit comfortably on the chair. Very stable. When Xiang Yu tried to lift the chair off the ground, the force he suffered increased by one: the force of the chair pulling his hand downward. This force was equal to and opposite to the pulling force he acted on the chair, although the support force of the chair on him also increased at this time. , but the sum of the three forces is still zero, and he still has to sit where he is. Likewise, the force on the chair remains balanced and always stays in place. Based on this analysis, the legend that Xiang Yu lifted himself is not true. People cannot lift themselves.