教学本课的目的,主要在于使学生了解水蒸发和沸腾的现象及其原因。让学生理解水蒸发的实质,是本课的重点。为完成这节课的教学任务,教师可在课前三天,将一瓶水放置在教室窗台上,要学生观察瓶子里水的变化,并指定一位同学每天定时把水面位置标在瓶子上。另外,教师课前还要准备好清水、火柴、试 The purpose of teaching this lesson is mainly to enable students to understand the phenomenon of water evaporation and boiling and its causes. Allow students to understand the essence of water evaporation is the focus of this lesson. To complete the teaching task of this lesson, teachers can place a bottle of water on the windowsill of the classroom three days before the class to observe the changes of the water in the bottle, and designate a classmate to regularly mark the water surface on the bottle every day . In addition, teachers have to prepare the water before class, matches, try