The plan motion of a free rigid body is analyzed from a video capture webcam. The absolute experimental trajectories of two points of the body allow to determine the relative trajectory of a point from the other point. The kinematic characteristics: speed, instantaneous speed of rotation, the initial kinematic conditions (positions, velocities) are determined by the inverse method from a Maple procedure based on nonlinear adjustment of Statistic package. The trajectories obtained are in good agreement with theoretical predictions. The law of transformation of velocities change is fully verified.