Often, in applications, springs are placed in combination. It is convenient, for purposes of
modeling and analysis, to replace the combination of springs by a single spring of an equivalent
stiffness, keq. The equivalent stiffness is determined such that the system with a combination
of springs has the same displacement, x, as the equivalent system when both
systems are subject to the same force, F. A model SDOF system consisting of a block
attached to a spring of an equivalent stiffness is illustrated in Figure 2.8. The resultant force
acting on the block is
(