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Re: Definition of Unstable

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Stan -

How about:	

	"An equilibrium state is said to be stable when small
	departures from equilibrium remain small with the lapse
	of time, and unstable when arbitrarily small initial
	deviations from equilibrium can ultimately become quite
	large."

	Birkhoff, G. and Rota, G.-C.  (1962)  Ordinary Differential
	Equations.  Ginn and Company:  New York, p. 81.

Garrett Birkhoff is late (d. 1998) Professor of Mathematics
at Harvard and Gian-Carlo Rota is late (d. 1999) Professor
of Applied Mathematics and Philosophy at MIT.

Alternatively, in reference to Euler column buckling:

	"For the ideal case that we are discussing, the
	column is in equilibrium in the straight position, even when
	P is greater than Pcr.  However, the equilibrium is unstable,
	and the smallest imaginable disturbance will cause the
	column to deflect sideways;  the deflections will increase
	immediately and the column will collapse."

	Gere, J.M and Timoshenko, S.P.  (1984)  Mechanics of Materials.
	Second Edition.  PWS Engineering:  Boston, p. 554.
--
Charles Hamilton, PhD EIT               Faculty Fellow
Department of Civil and                 Phone: 949.824.3752
    Environmental Engineering           FAX:   949.824.2117
University of California, Irvine        Email: chamilto(--nospam--at)uci.edu



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