高中教材中演示牛顿第三定律是将两个弹簧秤联结在一起,用手拉弹簧秤时指针移动的示数来证明作用力和反作用力大小相等、方向相反。为了增大实验的观察空间及可见度,我将弹簧秤改制后再用投影仪演示:将两个弹簧秤的外壳拆去,将其刻度按原大小画在两张投影胶片上,把两个没有外壳 High school textbooks demonstrate that Newton’s third law is to link two spring scales together. When the spring scales are hand-pulled, the indicator moves to show that the force and reaction force are equal in magnitude and opposite in direction. In order to increase the observation space and visibility of the experiment, I modified the spring scale and then demonstrated it with a projector: Remove the housing of the two spring scales, draw the scale of the two scales on the two transparencies, and put the two without housing.