Experiments were conducted to measure the unsteady plunging forces on a NACA- 0012 airfoil at zero undisturbed flow velocity. The aim is to investigate the vari- ation of the added forces associated with high oscillation frequencies at various angles of attack. Data of the measured forces are presented and compared with the predicted forces from potential flow approximations. The results show a signifi- cant departure from those estimates particularly at high frequencies. The results show that the measured added forces varies in a cubic manner with the frequency of oscillations. These results were revealed to be different in its formulation com- pared to the formulation using Stokes flow. The measured forces were proposed to be a function of the local acceleration and drag forces that is function of the square of the wing section velocity.