Abstract
The purpose of this study is to know differences between steady and unsteady drag coefficients of a sphere. We propose a way based on the equation of motion to obtain the unsteady drag coefficient considering an added math. To confirm validity of the way, we measured experimentally the motion of the falling sphere in water by using a high-speed camera and a motion capture method. The drag coefficients as a function of time were obtained by substituting measured values of velocity and acceleration into the equation of motion. Comparing with the values obtained by the other previous studies, our result is reasonable.
