教“浮力”这一章节时,为了突出重点,我先出示三个外形完全相同的乒乓球(其中有两个用注射器注入适量的盐水),问学生:“把三个乒乓球同时浸在水中,是上浮,还是下沉呢?”学生异口同声说: “上浮。”“真的上浮吗?”在全班学生注意力集中的时候,我 When teaching the “buoyancy” chapter, in order to highlight the points, I first presented three identically shaped table tennis balls (two of which were filled with a proper amount of saline with a syringe) and asked the students: “Put three table tennis balls at the same time. In the water, is it floating or sinking?” The students said in unison: “Floating.” “Is it really floating?” When the attention of the whole class is focused, I