《反冲》一课通过两个实验引导学生进行观察、归纳、概括,从而建立初步的“反冲”概念。两个实验取材方便,造价低廉,准备容易,体现了变废为宝的节约性原则。但细究一番,两个实验却都有其不足之处:在第一个实验中,水从塑料瓶内流出还不到四分之一,水流方向不太明 The “Recoil” lesson guides students through two experiments to observe, summarize and summarize, so as to establish the initial concept of “recoil”. The two experimental materials convenient, low cost, ready for easy, embodies the principle of saving waste into treasure. However, a closer look, both experiments have their shortcomings: in the first experiment, water flow from the plastic bottle less than a quarter, the flow direction is not clear