文章采用球形雨滴模型，利用空气阻力系数CD的较严格的表达式即Wallis公式，计算出直径5 mm的雨滴在20 ℃的静止空气中自静止开始自由下落时的v~t图像．文章又在CD统一取作0.44的近似下，解出解析的、普适的v(t)函数，并作出相应的v~t图像．结果显示这两条v~t曲线几乎完全重合，这就意味着近似处理是完全合适的．文章解释了其中的原因，并指出实测极限速率比球形雨滴模型下的理论值小2.00 m/s的原因在于实际雨滴的形状呈现汉堡状，其实际的空气阻力系数经计算约为0.52．文章认为球形雨滴模型从总体上看是比较实用的．

The article adopts the spherical raindrop model and uses the strict expression of the air resistance coefficient CD, namely the Wallis formula, to calculate the v~t image of a raindrop with a diameter of 5 mm when it freely falls from rest in still air at 20 ℃. The article also solves the analytical and universal v(t) function under the approximation of CD being uniformly taken as 0.44, and produces the corresponding v~t image. The results show that these two v~t curves almost completely coincide, indicating that the approximate treatment is completely appropriate. The article explains the reason for this and points out the reason for the limit rate measured in the experiment is 2.00 m/s lower than the theoretical value under the spherical raindrop model is the actual raindrop shape presents a Hamburg shape, and its actual air resistance coefficient is calculated to be about 0.52. We believe that the spherical raindrop model is generally practical.