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一、平均速度与速度平均值中学物理课本中平均速度的定义是:“在变速直线运动中一段位移和发生这段位移所用时间的比值,叫做运动物体在这段时间内的平均速度”。接着又进一步说明平均速度的数值跟在哪一段位移上或者说在哪一段时间内计算平均速度有关系。这个说明对于正确理解和计算平均速度是有益的。但初学者常认为速度对位移的平均值和速度对时间(与位移相应)的平均值是相同的。而速度对位移的平均值在“场论”中会遇到。作为教师弄清平均速度,速度对位移的平均值及速度对时间(相应的位移内)的平均值的概念是必要的。
First, the average speed and speed averages The definition of the average speed in middle school physics textbooks is: “The ratio of the time taken for a displacement and the occurrence of this displacement in the linear motion of speed change is called the average speed of the moving object during this period of time.” Next, it is further explained that the value of the average speed is related to which segment of displacement or in which period the average speed is calculated. This explanation is useful for correctly understanding and calculating the average speed. However, beginners often think that the average value of velocity vs. displacement is the same as the average value of velocity over time (corresponding to displacement). The average of speed versus displacement is encountered in the “field theory.” As the teacher ascertains the average speed, the concept of the average value of speed versus displacement and the average of speed versus time (within the corresponding displacement) is necessary.