FirstEdition DUE TO THE necessity to save weight and materialin the
design ofmodern structures and machines, stability problems have become
increasingly im- portant. The classicalengineering approach to this type
of problem has been characterized by the tacit assumption that
structures are nongyroscopic conservative systems, that is,
bythegeneraladoptionofthemethodsdeveloped for this particular case.
During the last decades numerous stability problems of a more
complicated nature have become important, and it has therefore become
necessary to correlate the various types of problems with the ap-
proaches to be used in their solution. The principal object ofthis
little bookisthis correlation between the systems to be investigated and
the methods to be used for this purpose, In other words, our main
concern is the choice of a correct approach. It is evident that this
idea renders it necessary to distinguish between the various types of
problems or systems. At the same time the similarities and the
connections between apparently quite different problems will become
obvious, and it will be evident that there islittle differencebetween,
say, the buckling of a column, thecritical speed of a turbine shaft, and
the stability of an airplane, a control mechanism, or an electric
circuit.