学生由认识平面图形到认识立体图形,是空间观念的一次发展,也是认识上的一个飞跃。他们对什么是体积,为什么计算长方体的体积要用长、宽、高相乘,以及单位进率是千进位等问题,在理解上都感到困难.教学时,要从观察入手,从感知着眼,引导学生带着比较异同的目的进行观察、操作,又在观察、操作的基础上进行比较,从而把这部分知识学懂、学活. Students recognize the three-dimensional graphics from the graphic to understand, is a space concept of a development, but also a leap in understanding. They are difficult to understand because of the volume of what they are, and why they should be calculated in terms of the length, width and height multiplied by the length, width and height of the cuboid, and the rate of cadres in the unit. In teaching, we should start from observation, Guide students with more similar purposes with the observation, operation, but also on the basis of observation, the operation of comparison, so that this part of knowledge learn, learn to live.