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初二物理第108页实验“研究液体的压强与深度的关系”和第149页“研究物体浮在液面的条件”是两个难度大又很重要的学生分组实验,都需要平底玻璃试管,装入沙子,直立浮在水面上(如图1)。但由于玻璃密度较大,试管较重,沙放少了,试管歪倒,放多,就沉没,根本不能在水面直立。就是设法找装药的平底薄壁短试管,沙放到刚好能使试管在水面直立,而露出水面的管长最多只有2厘米左右。课本要求实验三次,则每次加沙只能控制在管子再下沉0.5厘米,因为露出部分太短。这就造成用直尺量度试管水上部分长度的困难,误差较大。而且学生稍不小心,试管就沉没。
The second day of the physical page 108 experiment “The relationship between the pressure and depth of the study liquid” and page 149 “The conditions of the object floating on the liquid surface” are two difficult and very important student grouping experiments, all need Flat-bottomed glass test tube, into the sand, upright floating on the water (Figure 1). However, due to the greater density of glass, the test tubes are heavier and the sand is less. The test tubes trip over, put more and sink, and cannot stand on the water at all. It is to try to find a flat-bottomed, thin-walled, short-tube test tube. The sand is placed so that the test tube can stand upright on the surface of the water. The length of the tube that emerges from the surface is only about 2 cm. Textbooks require three experiments. Each time Gaza can only control the sinking of 0.5 cm in the tube, because the exposed part is too short. This results in the difficulty of measuring the length of the water in the test tube with a ruler, and the error is large. And the student did not care, the test tube sank.