They say that the mechanical analogues of capacitors are springs, and
>of inductors are shock absorbers.
"They" are wrong.
Like shock absorbers, both capacitors and inductors can absorb "shock" (see power supplies) and like springs, both can store energy for later release (see resonant circuits) .
In lay terms -
There are several elements in linear mechanical systems:
-mass (qty of "material"),
-spring (converts kinetic to potential), -damping (converts kinetic to heat and deducts it from the mechanical sum),
-kinetic energy (energy from motion), and -potential energy (energy from position).
There are several analogous elements in electromagnetics:
-charge (qty of "material"),
-capacitor and inductor, (converts kinetic to potential),
-resistor (converts kinetic to heat and deducts that energy from the electrical sum)
-current (energy from motion of charge), and
-voltage (defined as the potential energy between two positions in a field)
But do springs/shock absorbers have any kind of frequency-dependent >behaviors?
not as theoretical elements, nor within their "normal" operating range. However, there are phenomena associated with springs and shocks that can affect natural frequency over time. One classic is the automobile front suspension, where loss of spring constant from fabrication-stress relaxation in the coils (about 40% loss over two years) causes less-tight-handling, which can be compensated back to near original by using a larger than original damping constant (heavy duty shock). (You can work it out from the equation fx^2 + cx + d, and there are a couple of papers from the 70s on it if you are not familiar with frequency equations)
In the real world, as the frequency increases, the mass of the spring itself enters into the system as a separate equation and creates tertiary resonance as well as effecting the original theoretical spring-mass assumptions (f=ma).
There are a couple of charts I have seen listing corresponding elements for linear mechancial, rotary mechanical, fluid power, air power, and electromagnetic/electrical, and their equations. Control engineers find them fairly useful.
hope it helps