九年制义务教育初中物理教材,在重点介绍匀速直线运动物体的速度基础上,提出了变速直线运动的平均速度概念,并且给出了它的计算公式,在“密度”教学中,若能使学生在对物质的密度有一个充分了解的基础上,介绍一下“物体的密度”(简称物体的密度),其对于教和学都有一定的意义。 The ninth-year compulsory education junior middle school physics textbook, based on the introduction of the speed of uniform linear motion objects, proposes the concept of the average speed of linear motion for speed change, and gives its calculation formula. In the teaching of “density” teaching, Students can have a full understanding of the density of matter and introduce the “density of objects” (referred to as the density of objects), which has a certain significance for teaching and learning.