The drag effect on a falling ball caused by air is a conventional subject in the most well-known textbooks of classical mechanics and fluid dynamics. Further, there are some papers that employ video analysis to track objects movements in the air making it possible to obtain position data as a function of time and its graphs. However, none of them addresses the case of a ball thrown downwards, maybe because this situation is neglected by textbooks or probably due to the experimental difficulty to perform this kind of launch manually. In this paper, both the fall and the vertical launch down of five different Styrofoam balls are filmed with an ordinary smartphone camera and analysed by using the free software Tracker. The position and velocities graphs depicted clearly the air drag effect on the ball’s movements. The entire raw data are compared with a theoretical model and therefore terminal and initial velocities can be extracted as adjusted parameters from simple mathematical fits. The Reynolds number and the drag coefficient calculated for each ball agree with those found in the literature.

空气对落球的阻力效应是经典力学和流体动力学最著名的教科书中的常规主题。此外，有一些论文采用视频分析来跟踪物体在空中的运动，从而可以获得作为时间函数的位置数据及其图表。然而，它们都没有解决向下抛球的情况，可能是因为教科书忽略了这种情况，或者可能是由于手动执行这种发射的实验困难。在本文中，五个不同的泡沫聚苯乙烯球的坠落和垂直发射均使用普通智能手机相机拍摄，并使用免费软件 Tracker 进行分析。位置和速度图清楚地描绘了空气阻力对球运动的影响。将整个原始数据与理论模型进行比较，因此可以从简单的数学拟合中提取终端速度和初始速度作为调整参数。为每个球计算的雷诺数和阻力系数与文献中发现的一致。