中国有句至理名言：“吃一堑，长一智。”这话一点不假。跌个跟头，虽要受点儿皮肉之苦，却也许会有助于你认清惯性这一物理现象。从跌倒的地方爬起来，揉一揉摔疼的肢体，同时想想刚刚为什么就会跌倒呢？是脚下一滑还是一绊？正是这一滑或一绊使得人体的上下部分的“步调”（ There is a well-known saying in China: “Eat a meal and grow up with wisdom.” This is true. Falling back and coming back, although suffering from some skin and fur, may help you to understand the physical phenomenon of inertia. Climb up from where you fell, knead your tumbling body, and think about why you just fell. Is it a slide or a foot? It is this slipping or slipping that makes the “step” of the upper and lower parts of the human body (