学习《热空气》一课前,我动员学生收集了一些塑料袋,准备上课实验用。在第一个班上课时,我给每个小组发了一个塑料袋。开始实验了,有的小组很快就让充满热空气的塑料袋升了起来,孩子们发出了一阵阵欢呼,而有的小组可能是不小心吧,不是把塑料袋烧破了,就是把塑料袋撕破了。他们 Before I learned “Hot Air”, I mobilized students to collect some plastic bags and prepare them for class experiments. In the first class, I gave each group a plastic bag. When the experiment started, some groups soon lifted the plastic bags filled with hot air, and the children cheered. Some groups may be careless. Instead of burning the plastic bag, the plastic Tear the bag they