A 40 dB 1000 Hz tone moves air atoms by only about one nanometer.

Evidence

For a 100 Hz, 100 dB tone, the displacement is 10 times larger and the acceleration is one-tenth as large as for a 1000 Hz, 100 dB tone. If I is 40 dB at 1000 Hz, a soft sound but still well above the threshold for hearing in a home environment, I = 10–8 W/m2, a million times smaller than for 100 dB. The displacement ξ is proportional to square root of the intensity, so ξ is 1000 times less at 40 dB than at 100 dB or at 1000 Hz ξ ~ 10–9 m—just one nanometer, or the width of a few atoms! — Eric J. Heller, Why You Hear What You Hear- An…, 242

Categorization

• CANDY: Great fact: a soft but audible sound moves air by the width of a few atoms.
• QUESTION: Implies that our hair cells and eardrum detect sub-nanometer displacements — a stunning sensitivity worth chasing.