Abstract: Software tracker is applied in measuring the viscosity coefficient of liquid oil by dropping ball.By video capture and motion analyze function build in tracker,the trajectory of the falling ball is obtained.Experimental uncertainty lurking in the traditional measuring process is revealed and analyzed.The motion and data analysis by tracker are accurate and visual.The results show that the tracker is capable in exploring more complicated motion of fluid.

Key words: software tracker, motion capture, falling ball, viscosity coefficient of liquid