When doing electrostatic demonstrations, the "grass ball" used is the particularly light "rush". Because it is very light, it is attracted or repelled by other charged objects after being charged, and it pulls it The angle between the line and the vertical line is larger, and the experimental effect is obvious. This kind of thing is rare now. Available in Chinese medicine stores. Tongcaoqiu has not been seen in middle school physics books for more than ten years (I have never seen it in an official textbook since I was in middle school). Maybe it was in a textbook a long time ago, but some teachers cherish old things. I like to put it into extracurricular exercises, and it even appears in exam papers in certain regions. After investigation, it was found that Tongcao balls were cut from the pith of the stems of Tongtuo wood. In physics, it is mainly used as light and small objects and used in small electrostatic experiments, such as demonstrating that charged bodies can attract light and small objects. Its quality is similar to the core of sorghum stalks and corn stalks. Today's physics textbooks have long replaced grass balls with small balls cut from plastic foam.