我们指导学生做下面的一道习题:“用两根都是628厘米长的铁丝,分别围成一个正方形和一个圆,哪个面积大?大多少?”(五年制十册27页)学生做完之后,我们演示了一个简单有趣的实验:先将一个方形铁框在肥皂液中浸一下,使整个铁框内蒙上一层肥皂膜,再将一条有固定长的柔软细丝的两头连接起来,围成一条有任意形状的封闭曲线,并将这条曲线轻轻地搁置在铁框内。问:“如果用小针将曲线内的肥皂薄膜刺破,想一想,这条曲线会变成什么形状?”学生议论了一番之后,异口同声地回答:“会变成一 We guide the students in one of the following exercises: “Use two wires of 628 cm in length to form a square and a circle, respectively, and which area is large? How many?” (Five-year ten-volume, 27 pages) Students finish After that, we demonstrated a simple and interesting experiment: first, a square iron frame was immersed in a soapy liquid so that the whole iron frame was covered with a layer of soap film, and then the two ends of a fixed long soft filament were connected together, Enclose a closed curve of arbitrary shape, and gently rest this curve in the iron frame. Q: “If a small needle punctures the soap film in the curve, think of it, what is the shape of the curve?” After the students discussed for some time, they answered in unison: "Will become a