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neutral equilibrium[′nü·trəl ‚ē·kwə′lib·rē·əm]
A property of the steady state of a system which exhibits neither instability nor stability according to the particular criterion under consideration; a disturbance introduced into such an equilibrium will thus be neither amplified nor damped. Also known as indifferent equilibrium.
i. In meteorology, it is that condition in which the observed lapse rate is equal to the dry adiabatic lapse rate. A parcel of dry air will remain at its new level once it is pushed up because its temperature will be the same as that of the surrounding air.
ii. In aerodynamics, it means that an aircraft will tend to stay in its most recently commanded attitude or condition, without oscillations, and it will neither tend to return to its previous state or diverge from its new attitude. Also called neutral equilibrium or neutral static stability.