The production mechanism of sound is described here and explicitly said that the sound is vibration only. Help students to contextualize it. 

Here we also touched the concept of "damping" without being explicitly used "the term" damping. We believe that students have experience of damping though they might not know the term "Damping". Our intention is not that they learn terminology but to understand that vibrations can be damped because of that we can not feel or observe them.

Damping means amplitude of the vibration becomes lesser. The amplitude become so less, that sound wave can not reach to us. Because of that we can not hear sound even though the frequency is in audible range.

There is a question at the end, we want that students explore it by themselves. You can guide them.