What is the difference between aerodynamic balancing & mass balancing?

Aerodynamic balancing is used for the measurement of the forces exerted on the surfaces of instruments exposed to flowing air; frequently used in tests made on models in wind tunnels. Whereas in Mass balancing the flutter occurs when the control surface is displaced from its intended deflection. Because the ailerons are on long, narrow wings which can twist under load, they are the surface most prone to oscillate.