Free moving, conductive particles are a well-known risk for flashover of gas insulated systems. Depending on the motion and the relative position of the particle to the electrodes, the particle emits a unique partial discharge (PD) pulse pattern in time domain, which provides characteristic pulse repetition rates and signal amplitudes. The very short rise time of PD pulses in SF6 causes electromagnetic waves, which are radiated into the GIS compartment and can be measured using UHF sensScope of this work is the characterization of both, the physical motion pattern and the according electromagnetic partial discharge activity of free moving particles in a conventional GIS arrangement under positive high DC stress. The influence of parameters such as particle length, particle mass, polarity and amplitude of the applied DC voltage on the motion behavior are evaluated. In particular, firefly motion at the positive electrode is investigated and its fundamental mechanism is addressed. Finally, the effect of this particle motion on the insulation strength of GIS is considered.