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初中物理第一册“液体对压强的传递”一节里,通过一个壁上有小孔的空心球装水加压的演示,得以“液体能够把它受到的压强向各个方向传递”的结论。这是帕斯卡定律的基础。液体传递的为什么是压强而不是压力,课本没有作过多的阐述。教学时如果照本宣科,学生印象是不深的,往往还错误地认为液体跟固体一样传递的也是压力。为了帮助学生建立正确的概念,我在讲授这节教材时,增加了一个如下的演示:将一个20毫升的不装针头的注射器吸进一些水,让出水口朝下,夹装在铁架台上;将另一个100毫升的注射器也吸进一些水,水的高度跟上一个注射器所装的水的高度大致相等,把它同样夹装在另一个铁架台上。然后两只手各拿一只500克重的砝码,同时放在注射器的两个活塞上。可以看到。小注射器喷出的水比较急,大注射器喷出的水比较缓。比较两个注射器喷出的水的急缓,可以知道传递到小注射器针孔处的压强较大,传递到大注射器针孔处的压强较小。因为大小注射器活塞所受的压
In the section “Transmission of Liquids to Pressure” in the first volume of junior high school physics, a demonstration that a hollow ball filled with water in a small hole in the wall is pressurized can be used to conclude that “the liquid can transmit the pressure it receives in all directions”. This is the basis of Pascal’s law. Why the liquid is pressure is not pressure, the textbook does not elaborate too much. When teaching according to the text, the student’s impression is not deep, and often mistakenly believes that the same liquid as the solid is also the pressure. In order to help students establish the correct concepts, I added a demonstration as follows when teaching this lesson: Inject a 20-mL needle-free syringe into some water, with the water outlet facing downward and clamped on the iron stand. The other 100 ml syringe is also sucked in some water, the height of the water is about the same as the height of the water filled by a syringe, and it is also clamped on another iron stand. Then each hand took a 500-gram weight and placed it on both pistons of the syringe. can be seen. The water ejected by the small syringe is relatively acute and the water ejected by the large syringe is relatively slow. Comparing the slowness of the water sprayed by the two syringes, it can be known that the pressure transmitted to the small syringe needle hole is greater, and the pressure transmitted to the large syringe needle hole is smaller. Because of the pressure on the size of the syringe piston