从模型构建的角度深度窥视空气阻力  

PROBE INTO AIR RESISTANCE FROM THE PERSPECTIVE OF MODEL CONSTRUCTION

作　　者：应发宝 YING Fabao(Beijing Zhongguancun Middle School, Beijing 100086)

机构地区：[1]北京市中关村中学,北京100086

出　　处：《物理与工程》2020年第3期47-49,54,共4页Physics and Engineering

基　　金：北京市海淀区“十三五”规划重点关注课题《基于核心素养发展的物理学科融合教育模式及实施途径的研究》HDGH20190037部分研究成果。

摘　　要：文章指出,如果运用2019年北京理综试卷第24题题干条件“大量气体分子在各方向运动的几率相等”(即考虑气体分子热运动)进行建模,可得出雨滴在任意下落速度时所受空气阻力的表达式都为f=k1v+k2v^2,而非标准答案中的f=k2v^2,更不是参考文献[1]中所说的“利用传统的分子碰撞模型计算出的空气阻力为f∝v”。对于真实的雨滴下落情景,如果从分子自由程的视角分析,恰恰是“不计气体分子热运动”进行建模,才能得出标准答案中的f∝v^2的结论,题干中“由于大量分子在各方向运动的几率相等”确为多余条件。This paper points out that if the question stem in the 24th problem of Science Test Paper of the 2019 National College Entrance Examination(Beijing),“a large number of gas molecules moving in all directions(i.e.considering the thermal motion of gas molecules)”,is used to construct model,it can be drawn that the expression of the air resistance of the raindrops at any falling speed is f=k1v+k2v^2,rather than the f=k2v^2 in the standard answer,even far from the“air resistance f∝v calculated by the traditional molecular collision model”as given in Reference 1.For the real raindrop drop scenario,if we analyze it from the perspective of the molecular free path,it is precisely the modeling of“thermal motion without gas molecules”that the conclusion of f∝v^2 in the standard answer can be obtained.In the stem of the question,“a large number of molecules have equal probability of moving in all directions”is an unnecessary condition.

关 键 词：空气阻力 理想气体模型 密集粒子流模型 

分 类 号：G63[文化科学—教育学]