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【片断一】(师生共同概括出“围成圆的曲线的长叫做圆的周长”)师:怎么来测量圆的周长呢?都需要什么工具?生1:可以用绳子测量。用绳子先绕圆形物体一周,然后用尺子量绳子的长度就是它的周长。生2:也可以采用在尺子上滚动的方法。先在圆形物体周长的某部位做个记号为起点,对准0刻度,开始滚动,一直滚到有记号的地方,它走过的距离就是圆的周长。师:概括得真好。下面请小组合作测量自带学具的周长。
[Piece a] (teachers and students altogether out of “round the curve of the circle called the circumference of the circle ”) Teacher: how to measure the circumference of the circle? What tools are needed? Health 1: can be measured with a rope . Use a rope to circle a circular object first, and then use a ruler to measure the length of the rope to its perimeter. Health 2: You can also use the method of rolling on the ruler. First of all a circular object in the circumference of a mark as a starting point, aligned 0 scale, began to scroll, has been rolled to a marked place, it is the distance traveled the circle circumference. Teacher: Summarized so nice. The following group to measure the circumference of their own learning tools.