The diploma thesis examines the dynamics of the flexible structure. More precisely, it deals with the cutting line used in string trimmers. Its activity is analyzed using the theory of the dynamics of a rigid body system – the line is divided into several parts, the necessary geometric and material properties are attributed to them, and the line’s physical and numerical model is made. Using obtained models and the Python software, a simulation was performed in the analysis phase. This simulation is described in the results section of the thesis. In there, an example of the line rotation with constant acceleration is presented and there is also discussed how the string responds to different strains.