Bob,
I've found it useful to try to explain electrical concepts by using mechanical 
analogy, people are more comfortable with things they can see. In the case of
controlled impedance, you might try explaining it in terms of damping forces on
a spring (ie, spring constant, spring tension, etc.).
The analogies may not be exact (actually the mathmatics is very similar),
but they will allow you to start to explain how impedance can affect resonance
and other critical performance factors.

Mitch Austin
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