In this study, experimental investigation compares the fluid forces and wake modes of a freely-vibrating circular cylinder and a VIV-trajectory-tracking cylinder. The free VIV response was modelled on a low-friction air bearing system in conjunction with water channel facilities exhibits classical three amplitude-response ("initial", "upper" and "lower") branches. Measurements of the fluid forces, cylinder displacement and the wake modes are simultaneously conducted. On the other hand, the forced vibration experiments were conducted using a realtime PID motion controller with very high accuracy. Compared to the previous work of a cylinder undergoing sinusoidallydriven oscillations, the present study provides a more accurate comparison between free and forced vibrations. The wake modes of the cylinder undergoing tracking motion show some remarkable similarities to the case of free vibration.