Inertia and momentum are not identical. One is a tendency, and the other is a measure.

And Kim, please stop thinking about Newton's balls!! :>)

Because the string has an elasticity to it, and the bow's horsehair has a kind of intermittent coefficient of friction as it moves across the string, the string (being held at both ends, is set vibrating, as you say, causing waves of compression and expansion in the atmosphere. These waves in turn excite membranes in ears and microphones. Those membranes ultimately are set up as electrical pulses in the nervous system. Those nervous system impulses reach the brain and cause myriad configurations of synapses to discharge. Those myriad combinations of discharge are experienced by the soul as great delight, without further mechanism.

And while the soul part ALSO operates perfectly well in a vacuum, the mechanisms from string through soundwaves do not!

:>)

A