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在讲浮力产生的原因(初二第六章第一节)时,有些教师常常会提出“如果浸在水中的物体不受水对物体下底表面向上的压力时,物体是否受到水对它的浮力?”这样一个问题,学生从理论上弄清楚这个问题之后,能用演示实验加以说明,无疑可以加深学生对问题的理解和记忆,通常用直径为2厘米左右的蜡烛来做石蜡不浮实验,这样是可以说明问题,但是,可见度小,向容器中倒水时蜡烛易晃动实验不易成功。如果改用4公分×4公分×7公分的木块在木块的下底表面封上石蜡,可以避免以上两个问题,可以起到较好的课堂效果,具体作法如下:
When talking about the causes of buoyancy (Chapter 6, Chapter 1, Section 1), some teachers often propose that if an object immersed in water is not subjected to water pressure on the bottom surface of the object, the object is exposed to water. Buoyancy?" Such a problem, students can theoretically explain this problem, can demonstrate with demonstration experiments, no doubt can deepen students’ understanding of the problem and memory, usually with a candle with a diameter of about 2 cm to do paraffin Floating experiment, this can explain the problem, but the visibility is small, and it is not easy to shake the candle when the water is poured into the container. If you use 4cm x 4cm x 7cm blocks to block paraffin on the bottom surface of the block, you can avoid the above two problems and you can have a good classroom effect. The specific methods are as follows: