In air-jet weft insertion, the weft yam is moved by the frictional drag between the air stream and the yam surface. This paper reports the computer simulation of this process in order to determine the motion of the yarn during weft insertion. Forces acting on the weft depend on time as well as the varying position of the weft during insertion. The mathematical model of the system is implemented with a worksheet, and the results are shown using a graphics package. These theoretical results are compared with those experimentally obtained for the weft yarn. Weft positions in the reed channel in relation to machine timing in terms of shaft degrees are measured by the stroboscope of the machine for several picks, and the average value is taken for each position. Weft speed is calculated based on this measurement.