取一只空眼药水玻璃瓶,在里面装进适量洗净吹干的小石子和一些碎石蜡,然后取一段长约4cm 的自行车上用的汽门芯胶管,把它的一端套在眼药瓶尖口上。为了使汽门芯胶管竖直和不漏进水,在汽门芯内插进一根火柴棒,这就成了一个比重计,结构如图所示。把比重计放入水中,增减小石子,使浮起的比重计水面刚好淹没在汽门芯的中 Take a glass bottle of empty eye drops, and put a small amount of washed dry pebbles and some paraffin wax in it. Take a length of about 4cm of the valve core hose on the bicycle, and put one end of it on the eyedrops. Bottle tip. In order to make the valve core hose vertical and not leak water, insert a matchstick into the valve core, which becomes a hydrometer, the structure as shown. Put the hydrometer into the water and increase the size of the stones so that the surface of the floating dynamometer is just submerged in the valve core.