Wall friction converts organized oscillating air motion into heat, damping sound

Evidence

The friction results from the effects of a layer of air near the walls. The air directly in contact with the wall is barely moving, because it keeps colliding with the wall, which is not moving at all. Just next to that is a layer of air that struggles to move a little more, but it keeps colliding with the air nearer to the wall, and so on. As these layers rub against each other, heat is generated as surely as when you rub your hands together vigorously. The heat comes at the expense of the organized motion of the air oscillating back and forth, slowing it down—a source of damping we call viscosity. — Eric J. Heller, Why You Hear What You Hear- An…, 1438

Categorization

• DEFINE: Defines viscosity as a source of acoustic damping via layered wall friction.
• XREF: connects to: Panel absorbers convert sound into internal friction and respond to pressure — David Howard, Jamie Angus, coustics and Psychoacoustics, 2100