Definitions

• Positive Static Stability. Positive static stability is the initial tendency to return to an undisturbed state after a disturbance. This concept is easily illustrated by the ball and bowl analogy. Placing a ball in the bottom of a bowl which is the right way up and then moving it from the base up one side and letting go will, after some oscillation, result in the ball ending up stationary back on the base. This is positive static stability.
• Negative Static Stability or Static Instability. If the bowl is inverted and a ball balanced on the top is disturbed sufficiently for it to accelerate down the side, it will keep moving until something gets in the way. This is negative static stability or static instability.
• Neutral Static Stability. If a ball on a level surface is pushed, it will move a little and then stop. This is neutral static stability.

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