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过去在课堂上演示“反冲运动”时,我们所利用的仪器是在一个小车上,装置一个大试管,内盛水,用橡皮塞盖紧,再利用小车上的酒精灯,把水煮沸,得到高压水蒸汽,由于水蒸汽的热膨胀,把橡皮塞向前方打出,此时可以看到小车的反冲。在实践过程中,感到这个仪器有很多缺点。第一:由于小车上装置了酒精灯和试管中之水,而使得小车系统的质量与橡皮塞质量的比值过大,因之小车的反冲速度过小,观察起来不显著。第二:当水蒸汽施于橡皮塞上的压力等于或略大于橡皮塞与试管间的摩擦力时,橡皮塞即行飞出,所以其速度不大。
In past demonstrations of “recoil movements” in class, the instrument we used was in a small vehicle, which contained a large test tube, which contained water, was tightly closed with a rubber stopper, and used the alcohol lamp on the trolley to put water in it. Boil, get high-pressure water vapor, due to the thermal expansion of water vapor, the rubber plug to play forward, you can see the car’s recoil. In practice, I feel that this instrument has many shortcomings. Firstly, because the alcohol lamp and the water in the test tube are installed on the trolley, the ratio of the quality of the trolley system to the quality of the rubber plug is too large, and the recoil speed of the trolley is too small to observe it. Second: When the pressure exerted by water vapor on the rubber plug is equal to or slightly larger than the friction between the rubber plug and the test tube, the rubber plug will fly out, so its speed is not great.