Resonance lowers impedance dramatically at an oscillator’s natural frequency

Evidence

Untethered coins on a table move along without hindrance (except for friction, which we have neglected so far) but many objects are tied down and experience a restoring force pulling them back if they are displaced. The concept of impedance applies, but now impedance can be high owing not only to large mass but also to large stiffness because of a spring, which also tends to keep speed low. A mass and spring can combine to make an oscillator that vibrates at a certain natural frequency; if you push back and forth at that frequency, the impedance is low even if the mass is large and the spring is strong, because the oscillator gets moving very fast. — Eric J. Heller, Why You Hear What You Hear- An…, 84

Categorization

• DEFINE: Clear, intuitive definition of how resonance and impedance relate; the ‘gets moving very fast’ intuition for why impedance dips.
• XREF: Foundational for why we hear what we hear: this is the mechanism behind tuned resonator/basilar-membrane responses in the ear.