#### Physical Perspective on Repeated Poles in the Mass-Spring System

In the physical system, dc and infinite frequency are in fact strange
cases. In the case of dc, for example, a nonzero constant force
implies that the mass is under constant acceleration. It is
therefore the case that its *velocity is linearly growing*. Our
simulation predicts this, since, using
Eq.(F.43) and Eq.(F.42),

The dc term is therefore accompanied by a linearly growing
term in the *physical mass velocity*. It is therefore
unavoidable that we have some means of producing an unbounded,
linearly growing output variable.

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Mass-Spring Boundedness in Reality

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A Signal Processing Perspective on Repeated Mass-Spring Poles