油库围墙上有“严禁烟火”四个大字，面粉加工厂围墙上也写有“严禁烟火”，前者学生能理解，后者有相当一部分学生认为没有必要．为了说明其必要性，直观地用实验解释，可用如下方法进行实验．取长约１．５米的大竹筒剖成五块竹片，一块用细铁丝扎牢成为一个直径约０．５米的 There are four characters of “no smoking” on the wall of the oil depot, and “no smoking” is also written on the wall of the flour mill. The former students can understand that the latter can be understood by a considerable number of students. In order to explain its necessity, it is intuitively explained by experiment. Experiments can be done as follows. Take a large bamboo tube about 1.5 meters long and cut it into five bamboo pieces, one piece of which is tied with a thin wire to a diameter of about 0.5 meters.